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Abstract:

Biomass conversion systems may incorporate integrated heat management to
operate more efficiently during biomass conversion. Biomass conversion
systems may comprise a first fluid circulation loop comprising a
hydrothermal digestion unit, and a first catalytic reduction reactor unit
in fluid communication with an inlet and an outlet of the hydrothermal
digestion unit; and a second fluid circulation loop comprising a reaction
product take-off line in fluid communication with the first fluid
circulation loop, a second catalytic reduction reactor unit in fluid
communication with the reaction product take-off line, and a recycle line
establishing fluid communication between the first fluid circulation loop
and an outlet of the second catalytic reduction reactor unit, where the
first catalytic reduction reactor unit contains at least one first
catalyst and the second catalytic reduction reactor unit contains at
least one second catalyst, each being capable of activating molecular
hydrogen.

Claims:

1. A biomass conversion system comprising: a first fluid circulation loop
comprising: a hydrothermal digestion unit; and a first catalytic
reduction reactor unit in fluid communication with an inlet and an outlet
of the hydrothermal digestion unit; wherein the first catalytic reduction
reactor unit contains at least one first catalyst that is capable of
activating molecular hydrogen; and a second fluid circulation loop
comprising: a reaction product take-off line in fluid communication with
the first fluid circulation loop; a second catalytic reduction reactor
unit in fluid communication with the reaction product take-off line;
wherein the second catalytic reduction reactor unit contains at least one
second catalyst that is capable of activating molecular hydrogen; and a
recycle line establishing fluid communication between the first fluid
circulation loop and an outlet of the second catalytic reduction reactor
unit.

4. The biomass conversion system of claim 3, wherein the at least one
first catalyst comprises a poison-tolerant catalyst.

5. The biomass conversion system of claim 3, wherein the at least one
first catalyst is regenerable when poisoned with nitrogen compound
impurities, sulfur compound impurities, or any combination thereof.

6. The biomass conversion system of claim 3, wherein the at least one
first catalyst comprises a sulfided catalyst.

7. The biomass conversion system of claim 3, wherein the at least one
second catalyst is not a poison-tolerant catalyst.

8. The biomass conversion system of claim 1, wherein the first fluid
circulation loop is configured to establish countercurrent flow in the
hydrothermal digestion unit.

9. The biomass conversion system of claim 1, further comprising: a
biomass feed mechanism operatively coupled to the hydrothermal digestion
unit that allows a cellulosic biomass to be continuously or
semi-continuously added to the hydrothermal digestion unit without the
hydrothermal digestion unit being depressurized.

10. The biomass conversion system of claim 1, further comprising: a phase
separation mechanism in fluid communication with the outlet of the second
catalytic reduction reactor unit.

11. The biomass conversion system of claim 1, further comprising: a phase
separation mechanism in fluid communication with an outlet of the first
catalytic reduction reactor unit.

12. The biomass conversion system of claim 1, further comprising: a flow
control mechanism associated with each fluid circulation loop that allows
a recycle ratio in each fluid circulation loop to be altered.

13. A method comprising: providing a biomass conversion system
comprising: a first fluid circulation loop comprising: a hydrothermal
digestion unit; and a first catalytic reduction reactor unit in fluid
communication with an inlet and an outlet of the hydrothermal digestion
unit; wherein the first catalytic reduction reactor unit contains at
least one first catalyst that is capable of activating molecular
hydrogen; and a second fluid circulation loop comprising: a reaction
product take-off line in fluid communication with the first fluid
circulation loop; a second catalytic reduction reactor unit in fluid
communication with the reaction product take-off line; wherein the second
catalytic reduction reactor unit contains at least one second catalyst
that is capable of activating molecular hydrogen; and a recycle line
establishing fluid communication between the first fluid circulation loop
and an outlet of the second catalytic reduction reactor unit; providing a
cellulosic biomass in the hydrothermal digestion unit; heating the
cellulosic biomass in the hydrothermal digestion unit to digest at least
a portion of the cellulosic biomass and form a hydrolysate comprising
soluble carbohydrates within a liquor phase; wherein at least about 70%
of the heat added to the cellulosic biomass in the hydrothermal digestion
unit is generated internally in the first catalytic reduction reactor
unit and the second catalytic reduction reactor unit; transferring at
least a portion of the liquor phase to the first catalytic reduction
reactor unit; forming a first reaction product in the first catalytic
reduction reactor unit; recirculating at least a portion of the liquor
phase to the hydrothermal digestion unit at a first flow rate; and
altering the first flow rate to increase or decrease a temperature of the
liquor phase in the first fluid circulation loop.

14. The method of claim 13, wherein heating the cellulosic biomass in the
hydrothermal digestion unit takes place at a pressure of at least about
30 bar.

15. The method of claim 13, wherein heating the cellulosic biomass in the
hydrothermal digestion unit takes place in the presence of an organic
solvent.

16. The method of claim 13, wherein the liquor phase is recirculated to
the hydrothermal digestion unit such that countercurrent flow is
established in the hydrothermal digestion unit.

17. The method of claim 13, wherein at least about 60% of the cellulosic
biomass, on a dry basis, is digested to produce hydrolysate.

18. The method of claim 13, wherein at least about 90% of the cellulosic
biomass, on a dry basis, is digested to produce hydrolysate.

19. The method of claim 13, wherein at least the at least one first
catalyst comprises a poison-tolerant catalyst.

20. The method of claim 13, wherein at least the at least one first
catalyst comprises a sulfided catalyst.

21. The method of claim 13, wherein the first flow rate is such that the
liquor phase spends about 3 hours or less in the hydrothermal digestion
unit before being transferred to the first catalytic reduction reactor
unit.

22. The method of claim 13, wherein the first flow rate is such that the
liquor phase is recirculated in the first fluid circulation loop at a
recycle ratio of at least about 2.

23. The method of claim 13, wherein the first flow rate is such that the
liquor phase is recirculated in the first fluid circulation loop at a
recycle ratio of up to about 20.

24. The method of claim 13, wherein the first flow rate is such that the
liquor phase is recirculated in the first fluid circulation loop at a
recycle ratio ranging between about 4 and about 10.

25. The method of claim 13, wherein providing a cellulosic biomass in the
hydrothermal digestion unit comprises continuously or semi-continuously
adding a cellulosic biomass to the hydrothermal digestion unit without
the hydrothermal digestion unit being depressurized.

26. The method of claim 25, wherein, after the cellulosic biomass is
added to the hydrothermal digestion unit, the pressure in the
hydrothermal digestion unit is at least about 30 bar.

27. The method of claim 13, wherein the liquor phase enters the first
catalytic reduction reactor unit at a temperature ranging between about
120.degree. C. and about 190.degree. C. and exits the first catalytic
reduction reactor unit at a temperature ranging between about 260.degree.
C. and about 275.degree. C.

28. The method of claim 13, further comprising: converting the first
reaction product into a biofuel.

29. The method of claim 13, further comprising: monitoring the
temperature of the liquor phase in the first fluid circulation loop.

30. The method of claim 13, further comprising: performing a phase
separation of the first reaction product to form an aqueous phase and an
organic phase; and recirculating the aqueous phase to the hydrothermal
digestion unit.

31. The method of claim 13, further comprising: transferring at least a
portion of the first reaction product to the second fluid circulation
loop; forming a second reaction product in the second catalytic reduction
reactor unit; and recirculating at least a portion of the second reaction
product to the first fluid circulation loop at a second flow rate.

32. The method of claim 31, further comprising: converting the second
reaction product into a biofuel.

33. The method of claim 31, further comprising: performing a phase
separation of the second reaction product to form an aqueous phase and an
organic phase.

34. The method of claim 33, further comprising: recirculating at least a
portion of the organic phase to the first fluid circulation loop.

35. The method of claim 31, wherein the second flow rate is such that the
second reaction product is recirculated to the first fluid circulation
loop at a recycle ratio of at least about 0.1.

36. The method of claim 31, wherein the second flow rate is such that the
second reaction product is recirculated to the first fluid circulation
loop at a recycle ratio ranging between about 0.1 and about 0.5.

37. The method of claim 31, wherein the second flow rate is such that a
sufficient quantity of the second reaction product is recirculated to the
first fluid circulation loop to inhibit lignins from precipitating.

38. The method of claim 31, wherein the second reaction product comprises
a higher percentage of organic compounds than it does water.

[0002] The present disclosure generally relates to the processing of
cellulosic biomass into biofuels, and, more specifically, to systems and
methods for processing biomass solids using integrated heat management
for process control.

BACKGROUND

[0003] Significant attention has been placed on developing alternative
energy sources to fossil fuels. One fossil fuel alternative having
significant potential is biomass, particularly cellulosic biomass such
as, for example, plant biomass. As used herein, the term "biomass" will
refer to a living or recently living biological material. Complex organic
molecules within biomass can be extracted and broken down into simpler
organic molecules, which may subsequently be processed through known
chemical transformations into industrial chemicals or fuel blends (i.e.,
a biofuel). In spite of biomass's potential in this regard, particularly
plant biomass, an energy- and cost-efficient process that enables the
conversion of biomass into such materials has yet to be realized.

[0004] Cellulosic biomass is the world's most abundant source of
carbohydrates due to the lignocellulosic materials located within the
cell walls of higher plants. Plant cell walls are divided into two
sections: primary cell walls and secondary cell walls. The primary cell
wall provides structural support for expanding cells and contains three
major polysaccharides (cellulose, pectin, and hemicellulose) and one
group of glycoproteins. The secondary cell wall, which is produced after
the cell has finished growing, also contains polysaccharides and is
strengthened through polymeric lignin covalently crosslinked to
hemicellulose. Hemicellulose and pectin are typically found in abundance,
but cellulose is the predominant polysaccharide and the most abundant
source of carbohydrates. Collectively, these materials will be referred
to herein as "cellulosic biomass."

[0005] Plants can store carbohydrates in forms such as, for example,
sugars, starches, celluloses, lignocelluloses, and/or hemicelluloses. Any
of these materials may represent a feedstock for conversion into
industrial chemicals or fuel blends. Carbohydrates can include
monosaccharides and/or polysaccharides. As used herein, the term
"monosaccharide" refers to hydroxy aldehydes or hydroxy ketones that
cannot be further hydrolyzed to simpler carbohydrates. Examples of
monosaccharides can include, for example, dextrose, glucose, fructose,
and galactose. As used herein, the term "polysaccharide" refers to
saccharides comprising two or more monosaccharides linked together by a
glycosidic bond. Examples of polysaccharides can include, for example,
sucrose, maltose, cellobiose, and lactose. Carbohydrates are produced
during photosynthesis, a process in which carbon dioxide is converted
into organic compounds as a way to store energy. This energy can be
released when the carbohydrates are oxidized to generate carbon dioxide
and water.

[0006] Despite their promise, the development and implementation of
bio-based fuel technology has been slow. A number of reasons exist for
this slow development. Ideally, a biofuel would be compatible with
existing engine technology and have capability of being distributed
through existing transportation infrastructure. Current industrial
processes for biofuel formation are limited to fermentation of sugars and
starches to ethanol, which competes with these materials as a food
source. In addition, ethanol has a low energy density when used as a
fuel. Although some compounds that have potential to serve as fuels can
be produced from biomass resources (e.g., ethanol, methanol, biodiesel,
Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane),
these fuels generally require new distribution infrastructure and/or
engine technologies to accommodate their physical characteristics. As
noted above, there has yet to be developed an industrially scalable
process that can convert biomass into fuel blends in a cost- and
energy-efficient manner that are similar to fossil fuels.

SUMMARY

[0007] The present disclosure generally relates to the processing of
cellulosic biomass into biofuels, and, more specifically, to systems and
methods for processing biomass solids using integrated heat management
for process control.

[0008] In some embodiments, the present invention provides a biomass
conversion system comprising: a first fluid circulation loop comprising:
a hydrothermal digestion unit; and a first catalytic reduction reactor
unit in fluid communication with an inlet and an outlet of the
hydrothermal digestion unit; wherein the first catalytic reduction
reactor unit contains at least one first catalyst that is capable of
activating molecular hydrogen; and a second fluid circulation loop
comprising: a reaction product take-off line in fluid communication with
the first fluid circulation loop; second catalytic reduction reactor unit
in fluid communication with the reaction product take-off line; wherein
the second catalytic reduction reactor unit contains at least one second
catalyst that is capable of activating molecular hydrogen; and a recycle
line establishing fluid communication between the first fluid circulation
loop and an outlet of the second catalytic reduction reactor unit.

[0009] In some embodiments, the present invention provides a method
comprising: providing a biomass conversion system comprising: a first
fluid circulation loop comprising: a hydrothermal digestion unit; and a
first catalytic reduction reactor unit in fluid communication with an
inlet and an outlet of the hydrothermal digestion unit; wherein the first
catalytic reduction reactor unit contains at least one first catalyst
that is capable of activating molecular hydrogen; and a second fluid
circulation loop comprising: a reaction product take-off line in fluid
communication with the first fluid circulation loop; a second catalytic
reduction reactor unit in fluid communication with the reaction product
take-off line; wherein the second catalytic reduction reactor unit
contains at least one second catalyst that is capable of activating
molecular hydrogen; and a recycle line establishing fluid communication
between the first fluid circulation loop and an outlet of the second
catalytic reduction reactor unit; providing a cellulosic biomass in the
hydrothermal digestion unit; heating the cellulosic biomass in the
hydrothermal digestion unit to digest at least a portion of the
cellulosic biomass and form a hydrolysate comprising soluble
carbohydrates within a liquor phase; wherein at least about 70% of the
heat added to the cellulosic biomass in the hydrothermal digestion unit
is generated internally in the first catalytic reduction reactor unit and
the second catalytic reduction reactor unit; transferring at least a
portion of the liquor phase to the first catalytic reduction reactor
unit; forming a first reaction product in the first catalytic reduction
reactor unit; recirculating at least a portion of the liquor phase to the
hydrothermal digestion unit at a first flow rate; and altering the first
flow rate to increase or decrease a temperature of the liquor phase in
the first fluid circulation loop.

[0010] The features and advantages of the present invention will be
readily apparent to one having ordinary skilled in the art upon a reading
of the description of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The following FIGURE is included to illustrate certain aspects of
the present invention, and should not be viewed as an exclusive
embodiment. The subject matter disclosed is capable of considerable
modifications, alterations, combinations, and equivalents in form and
function, as will occur to one having ordinary skill in the art and
having the benefit of this disclosure.

[0012] FIG. 1 shows a schematic of an illustrative biomass conversion
system of the present embodiments.

DETAILED DESCRIPTION

[0013] The present disclosure generally relates to the processing of
cellulosic biomass into biofuels, and, more specifically, to systems and
methods for processing biomass solids using integrated heat management
for process control.

[0014] Unless otherwise specified herein, it is to be understood that use
of the term "biomass" in the description that follows refers to
"cellulosic biomass solids." Solids may be in any size, shape, or form.
The cellulosic biomass solids may be natively present in any of these
solid sizes, shapes, or forms or may be further processed prior to
digestion in the embodiments described herein. The cellulosic biomass
solids may be present in a slurry form in the embodiments described
herein.

[0016] When converting biomass into industrial chemicals and fuel blends,
the complex organic molecules therein need to be broken down into simpler
molecules, which may be transformed into other compounds. For cellulosic
biomass, the first step in this process is the production of soluble
carbohydrates, typically by digestion. Digestion of cellulosic biomass
may be conducted using an acid or base in a kraft-like process at low
temperatures and pressures to produce a biomass pulp. These types of
digestion processes are commonly used in the paper and pulpwood industry.
According to the embodiments described herein, the digestion rate of
cellulosic biomass may be accelerated in the presence of a digestion
solvent at elevated temperatures and pressures that maintain the
digestion solvent in a liquid state above its normal boiling point. In
various embodiments, the digestion solvent may contain an organic
solvent, particularly an in situ-generated organic solvent, which may
provide particular advantages, as described hereinafter.

[0017] When biomass is processed into simpler molecules, a significant
portion of the biomass energy content may be consumed in the conversion
process. For example, energy may be expended during the separation and
removal of water, and for conversion reactions and separation steps. Use
of a digestion solvent at high temperatures and pressures may
significantly increase the energy input requirements for the conversion
process. If the energy input requirements for the digestion process
become too great, the economic feasibility of cellulosic biomass as a
feedstock material may be jeopardized. That is, if the energy input
needed to digest and convert cellulosic biomass is too great, processing
costs may become higher than the actual value of the product being
generated, and the net energy produced may be low. In order to keep
processing costs low and provide higher energy yields from the biomass,
the amount of externally added heat input to the digestion process should
be kept as low as possible while achieving as high as possible conversion
of the cellulosic biomass into soluble carbohydrates.

[0018] The present disclosure provides systems and methods that allow
cellulosic biomass to be efficiently digested to form soluble
carbohydrates, which may subsequently be converted through one or more
catalytic reduction reactions (e.g., hydrogenolysis and/or hydrogenation)
into reaction products comprising oxygenated intermediates that may be
further processed into higher hydrocarbons. The higher hydrocarbons may
be useful in forming industrial chemicals and transportation fuels (i.e.,
a biofuel), including, for example, synthetic gasoline, diesel fuels, jet
fuels, and the like. As used herein, the term "biofuel" will refer to any
transportation fuel formed from a biological source.

[0019] As used herein, the term "soluble carbohydrates" refers to
monosaccharides or polysaccharides that become solubilized in a digestion
process. As used herein, the term "oxygenated intermediates" refers to
alcohols, polyols, ketones, aldehydes, and mixtures thereof that are
produced from a catalytic reduction reaction (e.g., hydrogenolysis and/or
hydrogenation) of soluble carbohydrates. As used herein, the term "higher
hydrocarbons" refers to hydrocarbons having an oxygen to carbon ratio
less than that of at least one component of the biomass source from which
they are produced. As used herein, the term "hydrocarbon" refers to an
organic compound comprising primarily hydrogen and carbon, although
heteroatoms such as oxygen, nitrogen, sulfur, and/or phosphorus may be
present in some embodiments. Thus, the term "hydrocarbon" also
encompasses heteroatom-substituted compounds containing carbon, hydrogen,
and oxygen, for example.

[0020] Illustrative carbohydrates that may be present in cellulosic
biomass include, for example, sugars, sugar alcohols, celluloses,
lignocelluloses, hemicelluloses, and any combination thereof. Once
soluble carbohydrates have been removed from the biomass matrix through a
digestion process according to the embodiments described herein, the
soluble carbohydrates may be transformed into a reaction product
comprising oxygenated intermediates via a catalytic reduction reaction.
Until the soluble carbohydrates are transformed by the catalytic
reduction reaction, they are very reactive and may be subject to
degradation under the digestion conditions. For example, soluble
carbohydrates may degrade into insoluble byproducts such as, for example,
caramelans and other heavy ends degradation products that are not readily
transformable by further reactions into a biofuel. Such degradation
products may also be harmful to equipment used in the biomass processing.
According to the embodiments described herein, a liquor phase containing
the soluble carbohydrates may be circulated in one or more fluid
circulation loops to remove the soluble carbohydrates from the digestion
conditions and convert them into less reactive oxygenated intermediates
(i.e., reaction products) via catalytic reduction reactions in order to
limit their degradation.

[0021] In addition to limiting the degradation of soluble carbohydrates,
circulation of the liquor phase may present several additional process
advantages. One of these advantages is that the amount of external heat
input to the digestion process may be reduced. As previously noted,
energy input requirements for the effective digestion of cellulosic
biomass at high temperatures may jeopardize the economic viability of
this material as a biofuel feedstock. By coupling a digestion unit and a
catalytic reduction reactor unit together in a fluid circulation loop, as
described in the present embodiments, much more efficient heat
integration may be realized. Catalytic reduction reactions such as, for
example, hydrogenation reactions and/or hydrogenolysis reactions, are
exothermic processes that may supply their excess generated heat to the
endothermic digestion process when these processes are coupled together
in a fluid circulation loop. Thus, the need for external heat input to
drive the digestion process may be considerably lessened. Furthermore,
this represents an efficient use of the excess heat generated by the
catalytic reduction reaction, which would otherwise need to be dissipated
in some manner. According to some embodiments herein, at least about 50%
of the heat added to the digestion unit may come from the catalytic
reduction reaction. In some embodiments, at least about 60% of the heat
added to the digestion unit may come from the catalytic reduction
reaction. In some embodiments, at least about 70% of the heat added to
the digestion unit may come from the catalytic reduction reaction. In
some embodiments, at least about 80% of the heat added to the digestion
unit may come from the catalytic reduction reaction. Further discussion
of heat integration in the foregoing manner is discussed in greater
detail hereinbelow.

[0022] A leading advantage of the biomass conversion systems described
herein is that the systems are designed to favor a high conversion of
biomass into a hydrolysate comprising soluble carbohydrates, for
subsequent processing into a biofuel. The biomass conversion systems and
associated methods described herein are to be distinguished from those of
the paper and pulpwood industry, where the goal is to harvest partially
digested wood pulp, rather than obtaining high quantities of soluble
carbohydrates by digesting as much of the cellulosic biomass as possible.
In some embodiments, at least about 60% of the cellulosic biomass, on a
dry basis, may be digested to form a hydrolysate comprising soluble
carbohydrates. In other embodiments, at least about 90% of the cellulosic
biomass, on a dry basis, may be digested to form a hydrolysate comprising
soluble carbohydrates. The design and operation of the present systems
may enable such high conversion rates by minimizing the formation of
degradation products during the processing of biomass. As previously
noted the present systems and methods may achieve the foregoing in an
energy- and cost-efficient manner.

[0023] A further advantage of the embodiments described herein is that
they may address the issue of lignin precipitation in the reactor system,
while simultaneously addressing the foregoing issues of heat integration
and soluble carbohydrate degradation. Lignin is a hydrophobic biopolymer
comprising about 30% of the dry weight of cellulosic biomass. Lignin
cannot be directly converted into desired biofuel components via
digestion, since it does not comprise a carbohydrate backbone. Since
lignin is hydrophobic, it may precipitate if its concentration becomes
too high in an aqueous digestion solvent. Although the processes
described herein are favorable in that they may result in a high
conversion of cellulosic biomass into soluble materials suitable for
conversion into liquid biofuels, they may also result in high lignin
concentrations in the digestion solvent, which may result in
precipitation. Precipitation or deposition of lignin in the reactor
system may result in costly process downtime. Although the solubility of
lignin may be increased by adding an external organic solvent to an
aqueous digestion solvent, this approach may be inefficient in terms of
the above-noted process energy and heat input issues. This problem, among
others, has been solved in the present disclosure through forming an in
situ-generated organic solvent (i.e., a reaction product produced by a
catalytic reduction reaction) and recirculating the solvent within the
fluid circulation loop containing the digestion unit in order to address
the foregoing issue of lignin precipitation while not compromising the
heat integration of the process. A further description of the solution to
the foregoing process is provided in more detail hereinbelow.

[0024] According to the embodiments described herein, at least a portion
of a reaction product (i.e., oxygenated intermediates) produced from a
catalytic reduction reactor unit within a fluid circulation loop may be
recirculated to a digestion unit contained within the fluid circulation
loop. As described above, this approach may minimize soluble carbohydrate
degradation and improve heat integration. The remainder of the reaction
product may be withdrawn from the fluid circulation loop and be
subsequently transformed. Specifically, at least a portion of the
reaction product may be transferred to another catalytic reduction
reactor unit within another fluid circulation loop in order to further
transform the reaction product. For example, the subsequent catalytic
reduction reaction unit may transform any soluble carbohydrates not
previously converted into oxygenated intermediates and/or remove
additional oxygenated functionalities from the reaction product
previously produced. Optional separations of an organic phase from an
aqueous phase may take place after each catalytic reduction reaction,
which may increase the organic solvent content of the reaction products.

[0025] According to the embodiments described herein, the foregoing fluid
circulation loops may be in fluid communication with one another. This
arrangement may allow at least a portion of the reaction product produced
in the second fluid circulation loop to be recirculated to the first
fluid circulation loop. Since the reaction product of the second fluid
circulation loop may be more highly enriched in organic solvents,
recirculating a portion of this reaction product to the first fluid
circulation loop may enhance lignin solubility without compromising heat
integration. In contrast, if an external organic solvent were added to
the first fluid circulation loop, it would need to be heated to maintain
the digestion rate, which would increase the energy costs of the process.
The remainder of the reaction product may be withdrawn from the second
fluid circulation loop and subsequently transformed to a biofuel.
Transformation into a biofuel may involve any combination of further
hydrogenolysis reactions, hydrogenation reactions, condensation
reactions, isomerization reactions, oligomerization reactions,
hydrotreating reactions, alkylation reactions, and the like.

[0026] In some embodiments, biomass conversion systems described herein
can comprise a first fluid circulation loop comprising: a hydrothermal
digestion unit; and a first catalytic reduction reactor unit in fluid
communication with an inlet and an outlet of the hydrothermal digestion
unit; wherein the first catalytic reduction reactor unit contains at
least one first catalyst that is capable of activating molecular
hydrogen; and a second fluid circulation loop comprising: a reaction
product take-off line in fluid communication with the first fluid
circulation loop; a second catalytic reduction reactor unit in fluid
communication with the reaction product take-off line; wherein the second
catalytic reduction reactor unit contains at least one second catalyst
that is capable of activating molecular hydrogen; and a recycle line
establishing fluid communication between the first fluid circulation loop
and an outlet of the second catalytic reduction reactor unit.

[0027] In some embodiments, the hydrothermal digestion unit may be, for
example, a pressure vessel of carbon steel, stainless steel, or a similar
alloy. In some embodiments, a single digestion unit may be used. In other
embodiments, multiple digestion units operating in series, parallel or
any combination thereof may be used. In some embodiments, digestion may
be conducted in a pressurized digestion unit operating continuously.
However, in other embodiments, digestion may be conducted in batch mode.
Suitable digestion units may include, for example, the "PANDIA®
Digester" (Voest-Alpine Industrienlagenbau GmbH, Linz, Austria), the
"DEFIBRATOR Digester" (Sunds Defibrator AB Corporation, Stockholm,
Sweden), the M&D (Messing & Durkee) digester (Bauer Brothers Company,
Springfield, Ohio, USA) and the KAMYR Digester (Andritz Inc., Glens
Falls, N.Y., USA). In some embodiments, the biomass may be at least
partially immersed in the digestion unit. In other embodiments, the
digestion unit may be operated as a trickle bed or pile-type digestion
unit. Fluidized bed and stirred contact digestion units may also be used
in some embodiments. Suitable digestion unit designs may include, for
example, co-current, countercurrent, stirred tank, or fluidized bed
digestion units.

[0028] In general, digestion may be conducted in a liquor phase. In some
embodiments, the liquor phase may comprise a digestion solvent that
comprises water. In some embodiments, the liquor phase may further
comprise an organic solvent. In some embodiments, the organic solvent may
comprise oxygenated intermediates produced from a catalytic reduction
reaction of soluble carbohydrates (i.e., a reaction product). For
example, in some embodiments, a digestion solvent may comprise oxygenated
intermediates produced by a hydrogenolysis reaction of soluble
carbohydrates. Such a hydrogenolysis reaction may take place in either or
both of the catalytic reduction reactor units described hereinabove.
Other organic solvents may be produced by conducting hydrogenation and/or
combined hydrogenolysis/hydrogenation in the catalytic reduction reactor
units. In some embodiments, bio-ethanol may be added to water as a
startup digestion solvent, with a solvent comprising oxygenated
intermediates being produced thereafter. Any other organic solvent that
is miscible with water may also be used as a startup digestion solvent,
if desired. In general, a sufficient amount of liquor phase is present in
the digestion process such that the biomass surface remains wetted. The
amount of liquor phase may be further chosen to maintain a sufficiently
high concentration of soluble carbohydrates to attain a desirably high
reaction rate during subsequent catalytic reduction, but not so high that
degradation becomes problematic. In some embodiments, the concentration
of soluble carbohydrates may be kept below about 5% by weight of the
liquor phase to minimize degradation. However, it is to be recognized
that higher concentrations may be used in some embodiments. In some
embodiments, organic acids such as, for example, acetic acid, oxalic
acid, acetylsalicylic acid, and acetylsalicylic acid may be included in
the liquor phase as an acid promoter of the digestion process.

[0029] In some embodiments, prior to digestion, the cellulosic biomass may
be washed and/or reduced in size (e.g., by chopping, crushing, debarking,
and the like) to achieve a desired size and quality for being digested.
These operations may remove substances that interfere with further
chemical transformations of soluble carbohydrates and/or improve
penetration of the digestion solvent into the biomass. In some
embodiments, washing may occur within the digestion unit prior to
pressurization. In other embodiments, washing may occur before the
biomass is placed in the digestion unit.

[0030] In some embodiments, the digestion solvent may comprise oxygenated
intermediates of an in situ-generated organic solvent. As used herein,
the term "in situ generated organic solvent" refers to the reaction
product produced from a catalytic reduction reaction of soluble
carbohydrates, where the catalytic reduction reaction takes place in a
catalytic reduction reactor unit coupled to the biomass conversion
system. In some embodiments, the in situ-generated organic solvent may
comprise at least one alcohol, ketone, or polyol. In alternative
embodiments, the digestion solvent may be at least partially supplied
from an external source. For example, in an embodiment, bio-ethanol may
be used to supplement the in situ-generated organic solvent. In some
embodiments, the digestion solvent may be separated, stored, or
selectively injected into the digestion unit so as to maintain a desired
concentration of soluble carbohydrates.

[0031] In some embodiments, digestion may take place over a period of time
at elevated temperatures and pressures. In some embodiments, digestion
may take place at a temperature ranging between about 100° C. to
about 240° C. for a period of time. In some embodiments, the
period of time may range between about 0.25 hours and about 24 hours. In
some embodiments, the digestion to produce soluble carbohydrates may
occur at a pressure ranging between about 1 bar (absolute) and about 100
bar.

[0033] Various factors may influence the digestion process. In some
embodiments, hemicellulose may be extracted from the biomass at
temperatures below about 160° C. to produce a predominantly
C5 carbohydrate fraction. At increasing temperatures, this C5
carbohydrate fraction may be thermally degraded. It may therefore be
advantageous to convert the C5 and/or C6 carbohydrates and/or
other sugar intermediates into more stable intermediates such as sugar
alcohols, alcohols, and polyols. By reacting the soluble carbohydrates in
a catalytic reduction reactor unit and recirculating at least a portion
of the reaction product to the digestion unit, the concentration of
oxygenated intermediates may be increased to commercially viable
concentrations while the concentration of soluble carbohydrates is kept
low.

[0034] In some embodiments, cellulose digestion may begin above about
160° C., with solubilization becoming complete at temperatures
around about 190° C., aided by organic acids (e.g., carboxylic
acids) formed from partial degradation of carbohydrate components. Some
lignins may be solubilized before cellulose, while other lignins may
persist to higher temperatures. These lignins may optionally be removed
at a later time. The digestion temperature may be chosen so that
carbohydrates are solubilized while limiting the formation of degradation
products.

[0035] In some embodiments, a plurality of digestion units may be used. In
such embodiments, the biomass may first be introduced into a digestion
unit operating at about 160° C. or below to solubilize C5
carbohydrates and some lignin without substantially degrading these
products. The remaining biomass may then exit the first digestion unit
and pass to a second digestion unit. The second digestion unit may be
used to solubilize C6 carbohydrates at a higher temperature. In
another embodiment, a series of digestion units may be used with an
increasing temperature profile, such that a desired carbohydrate fraction
is solubilized in each.

[0036] As previously described, one particularly advantageous feature of
the biomass conversion systems described herein is the heat integration
and management offered by re-circulating at least a portion of the
reaction product produced in the first catalytic reduction reactor unit
to the hydrothermal digestion unit. It should be noted, however, that
when utilizing this approach, purification of the hydrolysate is not
typically performed before the hydrolysate enters the first catalytic
reduction reactor unit, since conventional purification techniques such
as ion exchange and chromatographic separation techniques (e.g., size
exclusion, membrane separation, and the like) are often incompatible with
the high temperatures of the hydrolysate exiting the digestion unit. If
the hydrolysate were cooled (e.g., to less than 100° C.) to
conduct purification (e.g., by ion exchange or chromatographic
separation) and then reheated to the original temperature, the heat
integration benefits of the present embodiments could be at least
partially reduced. For an integrated process operating with a high
recirculation rate of solvent to minimize degradation of hydrolysate, the
additional process energy needed for reheating following purification may
represent a substantial portion of the heating value of the produced
biofuels. This may result in low energy yields for the process. However,
if purification of the hydrolysate is not performed, poisoning of the
catalyst in at least the first catalytic reduction reactor unit may
occur. Illustrative impurities that may poison catalysts used for
catalytic reduction reactions may include, for example, nitrogen compound
impurities, sulfur compound impurities, and any combination thereof. Such
impurities may be organic or inorganic in nature and may be natively
present in the cellulosic biomass or formed during the digestion process
used to produce soluble carbohydrates from cellulosic material, for
example.

[0037] In view of the advantages offered by heat integration, as described
herein, in some embodiments, the first fluid circulation loop may lack a
purification mechanism operable for removing nitrogen compound
impurities, sulfur compound impurities, or any combination thereof. That
is, in such embodiments, during the operation of the present biomass
conversion systems, a hydrolysate produced from the hydrothermal
digestion unit may not be purified prior to being transferred to the
first catalytic reduction reactor unit. To avoid catalyst poisoning in
such embodiments, a poison-tolerant catalyst may be used in at least the
first catalytic reduction reactor unit. As used herein, a
"poison-tolerant catalyst" is defined as a catalyst that is capable of
activating molecular hydrogen without needing to be regenerated or
replaced due to low catalytic activity for at least about 12 hours of
continuous operation. In some or other embodiments, a poison-tolerant
catalyst may also be used in the second catalytic reduction reactor unit.
In some embodiments, a poison-tolerant catalyst may be used in the first
catalytic reduction reactor unit and a conventional catalyst capable of
activating molecular hydrogen may be used in the second catalytic
reduction reactor unit. In some embodiments, a poison-tolerant catalyst
may be used in both the first catalytic reduction reactor unit and the
second catalytic reduction reactor unit. In some cases, a poison-tolerant
catalyst may produce a lower catalytic turnover rate than does a
conventional catalyst. Therefore, in embodiments in which a
poison-tolerant catalyst is used in the first catalytic reduction reactor
unit, it may be advantageous to use a higher activity conventional
catalyst in the second catalytic reduction reactor unit to complete the
reduction of soluble carbohydrates into a reaction product. It is
believed that any poisons present in the hydrolysate will primarily
interact with the catalyst in the first catalytic reduction reactor unit,
thereby allowing a conventional catalyst to be used in the second
catalytic reduction reactor unit with less risk of poisoning. In
alternative embodiments, a regenerable catalyst may be used in either
catalytic reduction reactor unit. As used herein, a "regenerable
catalyst" may have at least some of its catalytic activity restored
through regeneration, even when poisoned with nitrogen compound
impurities, sulfur compound impurities, or any combination thereof.
Ideally, such regenerable catalysts should be regenerable with a minimal
amount of process downtime.

[0038] In some embodiments, suitable poison-tolerant catalysts may
include, for example, a sulfided catalyst. Sulfided catalysts suitable
for activating molecular hydrogen are described in commonly owned U.S.
Patent Applications 61/496, 653, filed Jun. 14, 2011, and 61/553,591,
filed Oct. 31, 2011, each of which is incorporated herein by reference in
its entirety. Sulfiding may take place by treating a catalyst with
hydrogen sulfide, optionally while the catalyst is deposited on a solid
support. In more particular embodiments, the poison-tolerant catalyst may
be a sulfided cobalt-molybdate catalyst. We have found that sulfided
cobalt-molybdate catalysts may give a high yield of the desired
mono-oxygenate intermediates including C2-C6 alcohols and
ketones, while not forming an excess amount of C2-C4 alkanes.
The mono-oxygenated intermediates formed may be readily separated from
water via flash vaporization or liquid-liquid phase separation, and
undergo condensation-oligomerization reactions in separate steps over an
acid or base catalyst, to product liquid biofuels in the gasoline, jet,
or diesel range.

[0039] In general, the catalytic reduction reactor units used in
accordance with the embodiments described herein may be of any suitable
type or configuration. In some embodiments, at least one of the catalytic
reduction reactor units may comprise a fixed bed catalytic reactor such
as, for example, a trickle bed catalytic reactor. For example, in some
embodiments, the first catalytic reduction reactor unit may comprise a
fixed bed catalytic reactor. Other suitable catalytic reactors may
include, for example, slurry bed catalytic reactors with filtration, loop
reactors, upflow gas-liquid reactors, ebullating bed reactors, fluidized
bed reactors, and the like.

[0040] In some embodiments, the catalytic reduction reactions carried out
in the catalytic reduction reactor units may be hydrogenolysis reactions.
A further description of hydrogenolysis reactions follows.

[0041] Various processes are known for performing hydrogenolysis of
carbohydrates. One suitable method includes contacting a carbohydrate or
stable hydroxyl intermediate with hydrogen, optionally mixed with a
diluent gas, and a hydrogenolysis catalyst under conditions effective to
form a reaction product comprising oxygenated intermediates such as, for
example, smaller molecules or polyols. As used herein, the term "smaller
molecules or polyols" includes any molecule having a lower molecular
weight, which may include a smaller number of carbon atoms and/or oxygen
atoms, than the starting carbohydrate. In an embodiment, reaction
products of a hydrogenolysis reaction may include smaller molecules such
as, for example, polyols and alcohols. This aspect of hydrogenolysis
entails the breaking of carbon-carbon bonds

[0042] In an embodiment, a soluble carbohydrate may be converted to
relatively stable oxygenated intermediates such as, for example,
propylene glycol, ethylene glycol, and/or glycerol using a hydrogenolysis
reaction in the presence of a catalyst that is capable of activating
molecular hydrogen. Suitable catalysts may include, for example, Cr, Mo,
W, Re, Mn, Cu, Cd, Fe, Co, Ni, Pt, Pd, Rh, Ru, Ir, Os, and alloys or any
combination thereof, either alone or with promoters such as Au, Ag, Cr,
Zn, Mn, Sn, Bi, B, O, and alloys or any combination thereof. Other
suitable catalysts may include the poison-tolerant catalysts set forth
above. In some embodiments, the catalysts and promoters may allow for
hydrogenation and hydrogenolysis reactions to occur at the same time or
in succession. The catalyst may also include a carbonaceous pyropolymer
catalyst containing transition metals (e.g., chromium, molybdenum,
tungsten, rhenium, manganese, copper, and cadmium) or Group VIII metals
(e.g., iron, cobalt, nickel, platinum, palladium, rhodium, ruthenium,
iridium, and osmium). In certain embodiments, the catalyst may include
any of the above metals combined with an alkaline earth metal oxide or
adhered to a catalytically active support. In certain embodiments, the
catalyst used in the hydrogenolysis reaction may include a catalyst
support.

[0043] The conditions under which to carry out the hydrogenolysis reaction
may vary based on the type of biomass starting material and the desired
products (e.g., gasoline or diesel), for example. One of ordinary skill
in the art, with the benefit of this disclosure, will recognize the
appropriate conditions to use to carry out the reaction. In general, the
hydrogenolysis reaction may be conducted at temperatures in the range of
about 110° C. to about 300° C., preferably from about
170° C. to about 300° C., and most preferably from about
180° C. to about 290° C.

[0044] In an embodiment, the hydrogenolysis reaction may be conducted
under basic conditions, preferably at a pH of about 8 to about 13, and
even more preferably at a pH of about 10 to about 12. In an embodiment,
the hydrogenolysis reaction may be conducted at a pressure ranging
between about 1 bar (absolute) and about 150 bar, preferably at a
pressure ranging between about 15 bar and about 140 bar, and even more
preferably at a pressure ranging between about 50 bar and about 110 bar.

[0045] The hydrogen used in the hydrogenolysis reaction may include
external hydrogen, recycled hydrogen, in situ generated hydrogen, or any
combination thereof.

[0046] In some embodiments, the reaction products of the hydrogenolysis
reaction may comprise greater than about 25% by mole, or, alternatively,
greater than about 30% by mole of polyols, which may result in a greater
conversion to a biofuel in subsequent processing.

[0047] In some embodiments, hydrogenolysis may be conducted under neutral
or acidic conditions, as needed to accelerate hydrolysis reactions in
addition to the hydrogenolysis reaction. For example, hydrolysis of
oligomeric carbohydrates may be combined with hydrogenation to produce
sugar alcohols, which may undergo hydrogenolysis.

[0048] A second aspect of hydrogenolysis entails the breaking of --OH
bonds such as: RC(H)2--OH+H2→RCH3+H2O. This
reaction is also called "hydrodeoxygenation," and may occur in parallel
with C--C bond breaking hydrogenolysis. Diols may be converted to
mono-oxygenates via this reaction. As reaction severity is increased with
increasing temperature or contact time with the catalyst, the
concentration of polyols and diols relative to mono-oxygenates may
diminish as a result of hydrodeoxygenation. Selectivity for C--C vs.
C--OH bond hydrogenolysis may vary with catalyst type and formulation.
Full de-oxygenation to alkanes may also occur, but is generally
undesirable if the intent is to produce mono-oxygenates or diols and
polyols which may be condensed or oligomerized to higher molecular weight
compounds in during subsequent processing. Typically, it is desirable to
send only mono-oxygenates or diols to subsequent processing steps, as
higher polyols may lead to excessive coke formation during condensation
or oligomerization. Alkanes, in contrast, are essentially unreactive and
cannot be readily combined to produce higher molecular weight compounds.

[0049] Once oxygenated intermediates have been formed by a hydrogenolysis
reaction, a portion of the reaction product may be recirculated to the
digestion unit to serve as an internally generated digestion solvent.
Another portion of the reaction product may be withdrawn and subsequently
processed by further reforming reactions to form a biofuel or subjected
to further catalytic reduction reactions in another fluid circulation
loop. Before being withdrawn from the first fluid circulation loop, the
reaction product may optionally be separated into different components
(e.g., an aqueous phase and an organic phase). Suitable separation
mechanisms may include, for example, phase separation, solvent stripping
columns, extractors, filters, distillations and the like. In an
embodiment, azeotropic distillation may be used to affect separation. In
some embodiments, a separation of lignin from the reaction product may be
conducted before the reaction product is subsequently processed further
or recirculated to the digestion unit.

[0050] The embodiments described herein will now be further described with
reference to the drawing. FIG. 1 shows a schematic of an illustrative
biomass conversion system 1 corresponding to at least one of the present
embodiments. As depicted in FIG. 1, biomass conversion system 1 contains
first fluid circulation loop 10 and second fluid circulation loop 30.
First fluid circulation loop 10 contains hydrothermal digestion unit 12
and first catalytic reduction reactor unit 14 that are in fluid
communication with one another. Second fluid circulation loop 30 is in
fluid communication with first fluid circulation loop 10 and contains
reaction product take-off line 22, second catalytic reduction reactor
unit 24, and recycle line 26. Fluid communication of second fluid
circulation loop 30 with first fluid circulation loop 10 is established
via reaction product take-off line 22 and recycle line 26.

[0051] In some embodiments, the biomass conversion systems may further
comprise a biomass feed mechanism that is operatively coupled to the
hydrothermal digestion unit and allows a cellulosic biomass to be
continuously or semi-continuously added to the hydrothermal digestion
unit without the hydrothermal digestion unit being fully depressurized.
In some embodiments, the biomass feed mechanism may comprise a
pressurization zone. Cellulosic biomass may be pressurized using
pressurization zone 3 and then introduced to hydrothermal digestion unit
12 in a continuous or semi-continuous manner without fully depressurizing
the digestion unit. Pressurizing the cellulosic biomass prior to its
introduction to hydrothermal digestion unit 12 may allow the digestion
unit to remain pressurized and operating continuously during biomass
addition. Additional benefits of pressurizing the biomass prior to
digestion are also discussed hereinafter. As used herein, the term
"continuous addition" and grammatical equivalents thereof will refer to a
process in which biomass is added to a digestion unit in an uninterrupted
manner without fully depressurizing the digestion unit. As used herein,
the term "semi-continuous addition" and grammatical equivalents thereof
will refer to a discontinuous, but as-needed, addition of biomass to a
digestion unit without fully depressurizing the digestion unit.

[0052] During the operation of system 1, pressurization zone 3 may cycle
between a pressurized state and an at least partially depressurized
state, while hydrothermal digestion unit 12 remains continuously
operating in a pressurized state. While pressurization zone 3 is at least
partially depressurized, cellulosic biomass may be introduced to
pressurization zone 3 via loading mechanism 5. Suitable loading
mechanisms may include, for example, conveyer belts, vibrational tube
conveyers, screw feeders, bin dispensers, and the like. It is to be
recognized that, in some embodiments, loading mechanism 5 may be omitted.
For example, in some embodiments, addition of cellulosic biomass to
pressurization zone 3 may take place manually. Suitable types of
pressurization zones and operation thereof are described in commonly
owned U.S. Patent Applications Ser. Nos. 61/576,664 and 61/576,691, each
filed concurrently herewith and incorporated herein by reference in its
entirety.

[0053] In some embodiments, the cellulosic biomass within pressurization
zone 3 may be pressurized, at least in part, by introducing at least a
portion of the liquor phase in hydrothermal digestion unit 12 to
pressurization zone 3. In some or other embodiments, the cellulosic
biomass within pressurization zone 3 may be pressurized, at least in
part, by introducing a gas to pressurization zone 3. In some embodiments,
the liquor phase may comprise an organic solvent, which is generated as a
reaction product of first catalytic reduction reactor 14 and/or second
catalytic reduction reactor 24. In some embodiments, the liquor phase may
be transferred from hydrothermal digestion unit 12 to pressurization zone
3 by optional line 27. In some embodiments, system 1 may further include
optional line 25, which may transfer liquor phase internally within
hydrothermal digestion unit 12. Reasons why one would want to include
line 25 may include, for example, to maintain linear velocity of the
liquor phase in the digestion unit and to further manage the temperature
profile. In some or other embodiments, the liquor phase may be
transferred from a surge vessel (not shown) within first fluid
circulation loop 10.

[0054] At least two benefits may be realized by pressurizing the biomass
in the presence of the liquor phase. First, pressurizing the biomass in
the presence of the liquor phase may cause the digestion solvent to
infiltrate the biomass, which causes the biomass to sink in the digestion
solvent once introduced to the digestion solvent. Further, by adding hot
liquor phase to the biomass in pressurization zone 3, less energy needs
to be input to bring the biomass up to temperature once introduced to
hydrothermal digestion unit 12.

[0055] After introducing cellulosic biomass to hydrothermal digestion unit
12, the biomass may be heated under pressure in the presence of a
digestion solvent to produce a hydrolysate comprising soluble
carbohydrates. As the biomass is digested, the liquor phase containing
the hydrolysate is transported by line 16 to first catalytic reduction
reactor unit 14, where the soluble carbohydrates may be reduced to form
oxygenated intermediates (e.g., a first reaction product). For example,
in some embodiments, the soluble carbohydrates may be reduced via a
hydrogenolysis reaction. After oxygenated intermediates have been
produced, they may exit first catalytic reduction reactor 14 via line 18.
At this point, the liquor phase may either be recirculated to
hydrothermal digestion unit 12 via line 20 or transferred to second fluid
circulation loop 30 for further processing.

[0056] In some embodiments, the present biomass conversion systems may
further comprise phase separation mechanism 19 in fluid communication
with an outlet of first catalytic reduction reactor unit 14. In some
embodiments, the present biomass conversion systems may further comprise
phase separation mechanism 29 in fluid communication with an outlet of
second catalytic reduction reactor unit 24. In some embodiments, a phase
separation mechanism may be in fluid communication with both catalytic
reduction reactor units. Suitable phase separation mechanisms may include
for, example, phase separation, solvent stripping columns, extractors,
filters, distillations and the like. In an embodiment, azeotropic
distillation may be conducted.

[0057] When using a phase separation mechanism, the reaction product
produced from first catalytic reduction reactor unit 14 may be at least
partially separated into an aqueous phase and an organic phase prior to
being recirculated to hydrothermal digestion unit 12 or transferred to
second fluid circulation loop 30. In some embodiments, the aqueous phase
obtained from separation may be recirculated to hydrothermal digestion
unit 12, and the organic phase obtained from separation may be
transferred to second fluid circulation loop 30 for further processing.
In other embodiments, the organic phase or a mixed aqueous/organic phase
may be returned to hydrothermal digestion unit 12. Performing a
separation of the reaction product from first catalytic reduction reactor
unit 14 is one manner in which the fluid circulating in second fluid
circulation loop 30 may become more enriched in organic compounds. For
example, in some embodiments, the reaction product of second catalytic
reduction reactor unit 24 may contain a higher percentage of organic
compounds than it does water.

[0058] The liquor phase transferred to second fluid circulation loop 30
via reaction product take-off line 22 may comprise oxygenated
intermediates produced from first catalytic reduction reactor unit 14 and
any soluble carbohydrates that were not transformed. The liquor phase may
travel to second catalytic reduction reactor unit 24, where a second
catalytic reduction reaction may occur. For example, further
hydrogenolysis and/or hydrogenation may be conducted in second catalytic
reduction reactor unit 24. The catalytic reduction reaction that takes
place in second catalytic reduction reactor unit 24 may produce a second
reaction product that has less oxygenation and/or lower residual
untransformed soluble carbohydrates than the first reaction product, for
example.

[0059] Once the second reaction product exits second catalytic reduction
reactor unit 24, it may either be recirculated to first fluid circulation
loop 10 via recycle line 26 or removed from second fluid circulation loop
30 via reaction product take-off line 28. In some embodiments, at least a
portion of the second reaction product may be recirculated to first fluid
circulation loop 10. In some or other embodiments, at least a portion of
the second reaction product may be withdrawn from second fluid
circulation loop 30 and subsequently be transformed into a biofuel. A
description of the processes that may be used to form a biofuel are
described in further detail below.

[0060] In some embodiments, an optional separation of the second reaction
product may be performed using phase separation mechanism 29. Suitable
phase separation mechanisms may include those set forth above. In some
embodiments, the second reaction product may be at least partially
separated into an aqueous phase and an organic phase. In some
embodiments, the organic phase may be split, with at least a portion of
the organic phase being recirculated to first fluid circulation loop 10
and at least a portion of the organic phase being withdrawn via reaction
product take-off line 28. In some embodiments, the separated aqueous
phase may be discarded. In other embodiments, the separated aqueous phase
may be returned to first fluid circulation loop 10. As noted above,
recirculating an organic-rich phase to first fluid circulation loop 10
may be advantageous for inhibiting the precipitation of lignin.

[0061] In the embodiment depicted in FIG. 1, line 20 and hydrothermal
digestion unit 12 are configured such that countercurrent flow is
established within the digestion unit. As used herein, the term
"countercurrent flow" refers to the direction a reaction product enters
the hydrothermal digestion unit relative to the direction in which
biomass is introduced to the digestion unit. Although it may be
advantageous to establish countercurrent flow within hydrothermal
digestion unit 12, there is no requirement to do so. For example,
co-current flow may be established by connecting line 20 nearer the top
of hydrothermal digestion unit 12. However, establishing countercurrent
flow in hydrothermal digestion unit 12 may be beneficial in terms of
establishing a temperature gradient therein. This temperature gradient
may be beneficial for promoting the solubilization of carbohydrates, as
described hereinabove. Countercurrent flow may also be beneficial for
heat integration purposes, as the liquor phase will have a longer flow
pathway in hydrothermal digestion unit 12 over which to deposit its
excess heat than in other flow configurations.

[0062] In some embodiments, there may be a flow control mechanism
associated with each fluid circulation loop that allows a recycle ratio
in each fluid circulation loop to be altered. Still referring to FIG. 1,
first fluid circulation loop 10 and second fluid circulation loop 30 may
contain flow controllers 38 and 39, respectively. Flow controllers 38 and
39 may allow flow rates within each fluid circulation loop to be
regulated. Suitable flow controllers may include, for example, adjustable
flow restrictors, adjustable valves (e.g., gate, needle, diaphragm
valves), flow control valves, timed valves, timed flow splitter valves,
reflux splitters, and the like. By regulating the amount of liquor phase
being recirculated to hydrothermal digestion unit 12, the temperature
therein may be controlled, while still allowing sufficient reaction
product quantities to be withdrawn for subsequent processing into a
biofuel. Suitable flow rates and recycle ratios are considered in more
detail hereinbelow.

[0063] In some embodiments, the present biomass conversion systems may be
used for processing of cellulosic biomass into soluble carbohydrates and
oxygenated intermediates, which may be subsequently transformed into a
biofuel, for example. In some embodiments, the methods can comprise:
providing a biomass conversion system comprising: a first fluid
circulation loop comprising: a hydrothermal digestion unit; and a first
catalytic reduction reactor unit in fluid communication with an inlet and
an outlet of the hydrothermal digestion unit; wherein the first catalytic
reduction reactor unit contains at least one first catalyst that is
capable of activating molecular hydrogen; and a second fluid circulation
loop comprising: a reaction product take-off line in fluid communication
with the first fluid circulation loop; a second catalytic reduction
reactor unit in fluid communication with the reaction product take-off
line; wherein the second catalytic reduction reactor unit contains at
least one second catalyst that is capable of activating molecular
hydrogen; and a recycle line establishing fluid communication between the
first fluid circulation loop and an outlet of the second catalytic
reduction reactor unit; providing a cellulosic biomass in the
hydrothermal digestion unit; heating the cellulosic biomass in the
hydrothermal digestion unit to digest at least a portion of the
cellulosic biomass and form a hydrolysate comprising soluble
carbohydrates within a liquor phase; wherein at least about 70% of the
heat added to the cellulosic biomass in the hydrothermal digestion unit
is generated internally in the first catalytic reduction reactor unit and
the second catalytic reduction reactor unit; transferring at least a
portion of the liquor phase to the first catalytic reduction reactor
unit; forming a first reaction product in the first catalytic reduction
reactor unit; recirculating at least a portion of the liquor phase to the
hydrothermal digestion unit at a first flow rate; and altering the first
flow rate to increase or decrease a temperature of the liquor phase in
the first fluid circulation loop.

[0064] In some embodiments, providing a cellulosic biomass in the
hydrothermal digestion unit may comprise continuously or
semi-continuously adding a cellulosic biomass to the hydrothermal
digestion unit without the hydrothermal digestion unit being
depressurized, particularly to atmospheric pressure. In some embodiments,
after the cellulosic biomass is added to the hydrothermal digestion unit,
the pressure in the hydrothermal digestion unit may be at least about 30
bar. Further pressurization after addition of the biomass may take place,
if desired. In some embodiments, the hydrothermal digestion unit may be
at a pressure less than or equal to that of the pressurization zone used
to introduce the biomass into the digestion unit. In embodiments in which
the digestion unit pressure is lower than that of the pressurization
zone, the biomass and any liquor phase introduced to the pressurization
zone may surge into the digestion unit when pressure isolation between
the two is removed. In such embodiments, the digestion unit may be at a
higher pressure than it was prior to biomass addition. In other
embodiments, the pressure in the hydrothermal digestion unit may be
greater than or equal to that of the pressurization zone used to
introduce the biomass into the digestion unit. In embodiments in which
the digestion unit is at a higher pressure than the pressurization zone,
there may be a surge from the digestion unit into the pressurization zone
after pressure isolation between the two is removed, after which time at
least a portion of the biomass solids in the pressurization zone may
gravity drop into the digestion unit. In such embodiments, the digestion
unit may be at a lower pressure than it was prior to biomass addition.
Further, in such embodiments, the pressurization zone may serve dual in
digestion and biomass addition functions. Further details in this regard
are described in commonly owned U.S. Patent Applications Ser. Nos.
61/576,664 and 61/576,691, filed concurrently herewith, and previously
incorporated by reference hereinabove.

[0065] In some embodiments, the present methods may optionally further
comprise performing a phase separation of the first reaction product from
the first catalytic reduction reactor unit to form an aqueous phase and
an organic phase. In some embodiments, the aqueous phase may be
recirculated to the hydrothermal digestion unit. In some or other
embodiments, at least a portion of the organic phase may be recirculated
to the hydrothermal digestion unit. In still other embodiments, a mixed
aqueous phase/organic phase mixture may be recirculated to the
hydrothermal digestion unit. Suitable phase separation techniques have
been set forth hereinabove.

[0066] In some embodiments, the present methods may optionally further
comprise performing a phase separation of the second reaction product
from the second catalytic reduction reactor unit into an aqueous phase
and an organic phase. In some embodiments, the methods may further
comprise recirculating at least a portion of the organic phase to the
first fluid circulation line. In some embodiments, at least a portion of
the organic phase may be withdrawn from the second fluid circulation loop
and further converted into a biofuel. Suitable phase separation
techniques have been set forth hereinabove.

[0067] The reaction products produced from the catalytic reduction reactor
units may be converted into a biofuel according to the present
embodiments. Processes for converting the reaction products into a
biofuel are set forth in more detail hereinbelow. In some embodiments,
the first reaction product may be converted into a biofuel, where the
first reaction product is first subjected to a catalytic reduction
reaction in the second catalytic reduction reactor unit prior to being
converted into a biofuel. In some embodiments, the second reaction
product may be converted into a biofuel, as described in more detail
hereinbelow. Subsequent transformations for converting a reaction product
into a biofuel may include, for example, further catalytic reduction
reactions (e.g., hydrogenolysis reactions, hydrogenation reactions,
hydrotreating reactions, and the like), condensation reactions,
isomerization reactions, desulfurization reactions, dehydration
reactions, oligomerization reactions, alkylation reactions, and the like.

[0068] In some embodiments, the present methods may further comprise
transferring at least a portion of the first reaction product to the
second fluid circulation loop, forming a second reaction product in the
second catalytic reduction reactor unit, and recirculating at least a
portion of the second reaction product to the first fluid circulation
loop at a second flow rate. In some embodiments, the methods may further
comprise withdrawing at least a portion of the second reaction product
from the second fluid circulation loop. In some embodiments, the second
reaction product withdrawn from the second fluid circulation loop may be
converted into a biofuel.

[0069] By recirculating a liquor phase with the fluid circulation loops of
the present biomass conversion systems, more efficient digestion of
cellulosic biomass may be realized and degradation of soluble
carbohydrates may be lessened. Various recycle ratios within the first
and second fluid circulation loops may be used to accomplish the
foregoing. As used herein, the term "recycle ratio" will refer to the
amount of a liquor phase that is recirculated within a fluid circulation
loop relative to the amount of a liquor phase that is withdrawn from the
fluid circulation loop. By controlling recycle ratios according to the
present embodiments, temperature control of the liquor phase and
residence time of soluble carbohydrates within the hydrothermal digestion
unit may be controlled. In addition, by regulating the recycle ratios,
the relative composition of the liquor phase may be controlled,
particularly within the first fluid circulation loop. By controlling the
relative composition of the liquor phase, the risk of lignin
precipitation may be lessened, particularly within the first fluid
circulation loop. In various embodiments, the recycle ratios may be
regulated by controlling the flow rates within the fluid circulation
loops.

[0070] In some embodiments, the present methods may further comprise
monitoring the temperature of the liquor phase in the first fluid
circulation loop. As noted previously, the temperature may be increased
or decreased by altering the first flow rate within the first fluid
circulation loop. That is, by altering the recycle ratio within the first
fluid circulation loop, the temperature may be increased or decreased, as
desired. In some or other embodiments, the temperature in the first fluid
circulation loop may also be altered somewhat by adjusting the second
flow rate within the second fluid circulation loop. Generally, the
recycle ratio within the first fluid circulation loop is larger than that
within the second fluid circulation loop, as described below, and,
accordingly, the recycle ratio of the second fluid circulation loop may
have a lesser impact on temperature within the first fluid circulation
loop, since less liquor phase is being returned to the first fluid
circulation loop. By regulating the flow rates, in various embodiments,
the liquor phase may enter the first catalytic reduction reactor unit at
a temperature ranging between about 120° C. and about 190°
C. and exit the first catalytic reduction reactor unit at a temperature
ranging between about 260° C. and about 275° C. At these
temperatures, a pressure of at least about 30 bar may be present in the
hydrothermal digestion unit. As described above, the excess heat in the
liquor phase may be input to the digestion process. Further, the amount
of heat input may be regulated by controlling the recycle ratios of the
first fluid circulation loop and/or the second fluid circulation loop.

[0071] In some embodiments, the recycle ratio of the first fluid
circulation loop may be greater than that of the second fluid circulation
loop. By utilizing a high recycle ratio in the first fluid circulation
loop, degradation of soluble carbohydrates may be lessened by decreasing
the residence time of the liquor phase in the hydrothermal digestion
unit. In some embodiments, the first flow rate within the first fluid
circulation loop may be such that the liquor phase spends about 4 hours
or less in the hydrothermal digestion unit before being transferred to
the first catalytic reduction reactor unit. In some embodiments, the
first flow rate within the first fluid circulation loop is such that the
liquor phase spends about 3 hours or less in the hydrothermal digestion
unit before being transferred to the first catalytic reduction reactor
unit. In some embodiments, the first flow rate within the first fluid
circulation loop is such that the liquor phase spends about 2 hours or
less in the hydrothermal digestion unit before being transferred to the
first catalytic reduction reactor unit. In some embodiments, the first
flow rate within the first fluid circulation loop is such that the liquor
phase spends about 1 hour or less in the hydrothermal digestion unit
before being transferred to the first catalytic reduction reactor unit.
In some embodiments, the first flow rate within the first fluid
circulation loop is such that the liquor phase spends about 0.5 hours or
less in the hydrothermal digestion unit before being transferred to the
first catalytic reduction reactor unit.

[0072] In various embodiments, the recycle ratio within the first
circulation loop may range between about 2 and about 20. In some
embodiments, the first flow rate within the first fluid circulation loop
may be such that the liquor phase is recirculated in the first fluid
circulation loop at a recycle ratio of at least about 2. In some
embodiments, the first flow rate within the first fluid circulation loop
may be such that the liquor phase is recirculated in the first fluid
circulation loop at a recycle ratio of up to about 20. In some
embodiments, the first flow rate within the first fluid circulation loop
may be such that the liquor phase is recirculated in the first fluid
circulation loop at a recycle ratio ranging between about 4 and about 10.
As one of ordinary skill in the art will recognize, at higher recycle
ratios, there will be a greater opportunity for soluble carbohydrates
derived from cellulosic biomass to be transformed into a reaction
product, since the liquor phase will pass through the first catalytic
reduction reactor unit a greater number of times. Higher recycle ratios
also may be favorable for inhibiting the degradation of soluble
carbohydrates, as discussed above. As one of ordinary skill in the art
will further recognize, if the recycle ratio is too large, however, an
unsatisfactorily low amount of reaction product may be withdrawn from the
fluid circulation loop for subsequent processing into a biofuel. Given
the benefit of the present disclosure, one having ordinary skill in the
art will be able to determine an appropriate recycle ratio for the first
fluid circulation loop that achieves a desired amount of heat
integration, while balancing a desired rate of downstream biofuel
production.

[0073] In various embodiments, at least about 50% of the second reaction
product formed in the second catalytic reduction reactor unit may be
withdrawn from the second fluid circulation loop and further processed
into a biofuel, as described further hereinbelow. As in the first fluid
circulation loop, the recycle ratio may be regulated by controlling the
second flow rate in the second fluid circulation loop. In some
embodiments, at least about 10% of the second reaction product may be
recirculated to the first fluid circulation loop. In some embodiments,
the second flow rate in the second fluid circulation loop may be such
that the second reaction product is recirculated to the first fluid
circulation loop at a recycle ratio of at least about 0.1. In some or
other embodiments, the second flow rate in the second fluid circulation
loop may be such that the second reaction product is recirculated to the
first fluid circulation loop at a recycle ratio ranging between about 0.1
and about 0.5.

[0074] In some embodiments, the second reaction product being recirculated
to the first recirculation loop may comprise a higher percentage of
organic compounds than it does water. For example, a separation of the
reaction product may optionally take place after the first catalytic
reduction reaction unit and/or the second catalytic reduction reactor
unit. By using these optional separations, an aqueous stream that is
originally fairly dilute in organic compounds may be enriched to a stream
rich in organic compounds. Specifically, in some embodiments, the second
reaction product may comprise more organic compounds than it does water.

[0075] In some embodiments, the second flow rate in the second fluid
circulation loop may be such that a sufficient quantity of the second
reaction product is recirculated to the first fluid circulation loop to
inhibit lignins from precipitating. If the optional separation steps
described above are performed, the flow rate sufficient to maintain
lignin solubility will generally be lower, since the second reaction
product may be more enriched in organic solvents. In some embodiments, by
recirculating at least a portion of the second reaction product to the
first fluid circulation loop, the quantity of soluble lignins may be made
higher than if recirculation of the second reaction product were not
performed. In the event that the lignin concentration exceeds the
solubility limit, the present biomass conversion systems may also include
one or more lignin removal lines at any point in the first fluid
circulation loop.

[0076] In some embodiments, the methods described herein may further
comprise converting a hydrolysate comprising soluble carbohydrates into a
biofuel. In some embodiments, conversion of the hydrolysate into a
biofuel may begin with a first catalytic reduction reaction in the first
fluid circulation loop, as described above. In some embodiments,
conversion of the hydrolysate into a biofuel may continue with a second
catalytic reduction reaction, for example, in the second fluid
circulation loop, as described above. According to the present
embodiments, the reaction product from the second catalytic reduction
reaction may be further transformed by any number of further catalytic
reforming reactions including, for example, further catalytic reduction
reactions (e.g., hydrogenolysis reactions, hydrogenation reactions,
hydrotreating reactions, and the like), condensation reactions,
isomerization reactions, desulfurization reactions, dehydration
reactions, alkylation reactions, oligomerization reactions, and the like.
A description of some of these processes follows.

[0077] Oxygenated intermediates produced from a catalytic reduction
reaction may be processed to produce a fuel blend in one or more
processing reactions. In an embodiment, a condensation reaction may be
used along with other reactions to generate a fuel blend and may be
catalyzed by a catalyst comprising an acid, a base, or both. In general,
without being limited to any particular theory, it is believed that the
basic condensation reactions may involve a series of steps involving: (1)
an optional dehydrogenation reaction; (2) an optional dehydration
reaction that may be acid catalyzed; (3) an aldol condensation reaction;
(4) an optional ketonization reaction; (5) an optional furanic ring
opening reaction; (6) hydrogenation of the resulting condensation
products to form a ≧C4 hydrocarbon; and (7) any combination
thereof. Acid catalyzed condensations may similarly entail optional
hydrogenation or dehydrogenation reactions, dehydration, and
oligomerization reactions. Additional polishing reactions may also be
used to conform the product to a specific fuel standard, including
reactions conducted in the presence of hydrogen and a hydrogenation
catalyst to remove functional groups from final fuel product. In some
embodiments, a basic catalyst, a catalyst having both an acid and a base
functional site, and optionally comprising a metal function, may also be
used to effect the condensation reaction.

[0078] In some embodiments, an aldol condensation reaction may be used to
produce a fuel blend meeting the requirements for a diesel fuel or jet
fuel. Traditional diesel fuels are petroleum distillates rich in
paraffinic hydrocarbons. They have boiling ranges as broad as 187°
C. to 417° C., which are suitable for combustion in a compression
ignition engine, such as a diesel engine vehicle. The American Society of
Testing and Materials (ASTM) establishes the grade of diesel according to
the boiling range, along with allowable ranges of other fuel properties,
such as cetane number, cloud point, flash point, viscosity, aniline
point, sulfur content, water content, ash content, copper strip
corrosion, and carbon residue. Thus, any fuel blend meeting ASTM D975 may
be defined as diesel fuel.

[0079] The present disclosure also provides methods to produce jet fuel.
Jet fuel is clear to straw colored. The most common fuel is an
unleaded/paraffin oil-based fuel classified as Aeroplane A-1, which is
produced to an internationally standardized set of specifications. Jet
fuel is a mixture of a large number of different hydrocarbons, possibly
as many as a thousand or more. The range of their sizes (molecular
weights or carbon numbers) is restricted by the requirements for the
product, for example, freezing point or smoke point. Kerosene-type
Airplane fuel (including Jet A and Jet A-1) has a carbon number
distribution between about C8 and C16. Wide-cut or naphtha-type Airplane
fuel (including Jet B) typically has a carbon number distribution between
about C5 and C15. A fuel blend meeting ASTM D1655 may be defined as jet
fuel.

[0080] In certain embodiments, both Airplanes (Jet A and Jet B) contain a
number of additives. Useful additives include, but are not limited to,
antioxidants, antistatic agents, corrosion inhibitors, and fuel system
icing inhibitor (FSII) agents. Antioxidants prevent gumming and usually,
are based on alkylated phenols, for example, AO-30, AO-31, or AO-37.
Antistatic agents dissipate static electricity and prevent sparking.
Stadis 450 with dinonylnaphthylsulfonic acid (DINNSA) as the active
ingredient, is an example. Corrosion inhibitors (e.g., DCI-4A) are used
for civilian and military fuels, and DCI-6A is used for military fuels.
FSII agents, include, for example, Di-EGME.

[0081] In some embodiments, the oxygenated intermediates may comprise a
carbonyl-containing compound that may take part in a base catalyzed
condensation reaction. In some embodiments, an optional dehydrogenation
reaction may be used to increase the amount of carbonyl-containing
compounds in the oxygenated intermediate stream to be used as a feed to
the condensation reaction. In these embodiments, the oxygenated
intermediates and/or a portion of the bio-based feedstock stream may be
dehydrogenated in the presence of a catalyst.

[0082] In some embodiments, a dehydrogenation catalyst may be preferred
for an oxygenated intermediate stream comprising alcohols, diols, and
triols. In general, alcohols cannot participate in aldol condensation
directly. The hydroxyl group or groups present may be converted into
carbonyls (e.g., aldehydes, ketones, etc.) in order to participate in an
aldol condensation reaction. A dehydrogenation catalyst may be included
to effect dehydrogenation of any alcohols, diols, or polyols present to
form ketones and aldehydes. The dehydration catalyst is typically formed
from the same metals as used for hydrogenation, hydrogenolysis, or
aqueous phase reforming. These catalysts are described in more detail
above. Dehydrogenation yields may be enhanced by the removal or
consumption of hydrogen as it forms during the reaction. The
dehydrogenation step may be carried out as a separate reaction step
before an aldol condensation reaction, or the dehydrogenation reaction
may be carried out in concert with the aldol condensation reaction. For
concerted dehydrogenation and aldol condensation reactions, the
dehydrogenation and aldol condensation functions may take place on the
same catalyst. For example, a metal hydrogenation/dehydrogenation
functionality may be present on catalyst comprising a basic
functionality.

[0083] The dehydrogenation reaction may result in the production of a
carbonyl-containing compound. Suitable carbonyl-containing compounds may
include, but are not limited to, any compound comprising a carbonyl
functional group that may form carbanion species or may react in a
condensation reaction with a carbanion species. In an embodiment, a
carbonyl-containing compound may include, but is not limited to, ketones,
aldehydes, furfurals, hydroxy carboxylic acids, and, carboxylic acids.
Ketones may include, without limitation, hydroxyketones, cyclic ketones,
diketones, acetone, propanone, 2-oxopropanal, butanone, butane-2,3-dione,
3-hydroxybutane-2-one, pentanone, cyclopentanone, pentane-2,3-dione,
pentane-2,4-dione, hexanone, cyclohexanone, 2-methyl-cyclopentanone,
heptanone, octanone, nonanone, decanone, undecanone, dodecanone,
methylglyoxal, butanedione, pentanedione, diketohexane, dihydroxyacetone,
and isomers thereof. Aldehydes may include, without limitation,
hydroxyaldehydes, acetaldehyde, glyceraldehyde, propionaldehyde,
butyraldehyde, pentanal, hexanal, heptanal, octanal, nonal, decanal,
undecanal, dodecanal, and isomers thereof. Carboxylic acids may include,
without limitation, formic acid, acetic acid, propionic acid, butanoic
acid, pentanoic acid, hexanoic acid, heptanoic acid, isomers and
derivatives thereof, including hydroxylated derivatives, such as
2-hydroxybutanoic acid and lactic acid. Furfurals may include, without
limitation, hydroxylmethylfurfural, 5-hydroxymethyl-2(5H)-furanone,
dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydro-2-furoic acid,
dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydrofurfuryl alcohol,
1-(2-furyl)ethanol, hydroxymethyltetrahydrofurfural, and isomers thereof.
In an embodiment, the dehydrogenation reaction may result in the
production of a carbonyl-containing compound that is combined with the
oxygenated intermediates to become a part of the oxygenated intermediates
fed to the condensation reaction.

[0085] In some embodiments, the dehydration reaction may occur in the
vapor phase. In other embodiments, the dehydration reaction may occur in
the liquid phase. For liquid phase dehydration reactions, an aqueous
solution may be used to carry out the reaction. In an embodiment, other
solvents in addition to water, may be used to form the aqueous solution.
For example, water soluble organic solvents may be present. Suitable
solvents may include, but are not limited to, hydroxymethylfurfural
(HMF), dimethylsulfoxide (DMSO), 1-methyl-n-pyrollidone (NMP), and any
combination thereof. Other suitable aprotic solvents may also be used
alone or in combination with any of these solvents.

[0086] In an embodiment, the processing reactions may comprise an optional
ketonization reaction. A ketonization reaction may increase the number of
ketone functional groups within at least a portion of the oxygenated
intermediates. For example, an alcohol may be converted into a ketone in
a ketonization reaction. Ketonization may be carried out in the presence
of a basic catalyst. Any of the basic catalysts described above as the
basic component of the aldol condensation reaction may be used to effect
a ketonization reaction. Suitable reaction conditions are known to one of
ordinary skill in the art and generally correspond to the reaction
conditions listed above with respect to the aldol condensation reaction.
The ketonization reaction may be carried out as a separate reaction step,
or it may be carried out in concert with the aldol condensation reaction.
The inclusion of a basic functional site on the aldol condensation
catalyst may result in concerted ketonization and aldol condensation
reactions.

[0087] In an embodiment, the processing reactions may comprise an optional
furanic ring opening reaction. A furanic ring opening reaction may result
in the conversion of at least a portion of any oxygenated intermediates
comprising a furanic ring into compounds that are more reactive in an
aldol condensation reaction. A furanic ring opening reaction may be
carried out in the presence of an acidic catalyst. Any of the acid
catalysts described above as the acid component of the aldol condensation
reaction may be used to effect a furanic ring opening reaction. Suitable
reaction conditions are known to one of ordinary skill in the art and
generally correspond to the reaction conditions listed above with respect
to the aldol condensation reaction. The furanic ring opening reaction may
be carried out as a separate reaction step, or it may be carried out in
concert with the aldol condensation reaction. The inclusion of an acid
functional site on the aldol condensation catalyst may result in a
concerted furanic ring opening reaction and aldol condensation reactions.
Such an embodiment may be advantageous as any furanic rings may be opened
in the presence of an acid functionality and reacted in an aldol
condensation reaction using a basic functionality. Such a concerted
reaction scheme may allow for the production of a greater amount of
higher hydrocarbons to be formed for a given oxygenated intermediate
feed.

[0088] In an embodiment, production of a ≧C4 compound may
occur by condensation, which may include aldol condensation of the
oxygenated intermediates in the presence of a condensation catalyst.
Aldol-condensation generally involves the carbon-carbon coupling between
two compounds, at least one of which may contain a carbonyl group, to
form a larger organic molecule. For example, acetone may react with
hydroxymethylfurfural to form a C9 species, which may subsequently
react with another hydroxymethylfurfural molecule to form a C15
species. In various embodiments, the reaction is usually carried out in
the presence of a condensation catalyst. The condensation reaction may be
carried out in the vapor or liquid phase. In an embodiment, the reaction
may take place at a temperature ranging from about 7° C. to about
377° C. depending on the reactivity of the carbonyl group.

[0089] The condensation catalyst will generally be a catalyst capable of
forming longer chain compounds by linking two molecules through a new
carbon-carbon bond, such as a basic catalyst, a multi-functional catalyst
having both acid and base functionalities, or either type of catalyst
also comprising an optional metal functionality. In an embodiment, the
multi-functional catalyst may be a catalyst having both a strong acid and
a strong base functionalities. In an embodiment, aldol catalysts may
comprise Li, Na, K, Cs, B, Rb, Mg, Ca, Sr, Si, Ba, Al, Zn, Ce, La, Y, Sc,
Y, Zr, Ti, hydrotalcite, zinc-aluminate, phosphate, base-treated
aluminosilicate zeolite, a basic resin, basic nitride, alloys or any
combination thereof. In an embodiment, the base catalyst may also
comprise an oxide of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn, Re, Al, Ga, In,
Co, Ni, Si, Cu, Zn, Sn, Cd, Mg, P, Fe, or any combination thereof. In an
embodiment, the condensation catalyst comprises mixed-oxide base
catalysts. Suitable mixed-oxide base catalysts may comprise a combination
of magnesium, zirconium, and oxygen, which may comprise, without
limitation: Si--Mg--O, Mg--Ti--O, Y--Mg--O, Y--Zr--O, Ti--Zr--O,
Ce--Zr--O, Ce--Mg--O, Ca--Zr--O, La--Zr--O, B--Zr--O, La--Ti--O,
B--Ti--O, and any combinations thereof. Different atomic ratios of Mg/Zr
or the combinations of various other elements constituting the mixed
oxide catalyst may be used ranging from about 0.01 to about 50. In an
embodiment, the condensation catalyst may further include a metal or
alloys comprising metals, such as Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd,
Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Bi, Pb, Os, alloys and
combinations thereof. Such metals may be preferred when a dehydrogenation
reaction is to be carried out in concert with the aldol condensation
reaction. In an embodiment, preferred Group IA materials may include Li,
Na, K, Cs and Rb. In an embodiment, preferred Group IIA materials may
include Mg, Ca, Sr and Ba. In an embodiment, Group IIB materials may
include Zn and Cd. In an embodiment, Group IIIB materials may include Y
and La. Basic resins may include resins that exhibit basic functionality.
The basic catalyst may be self-supporting or adhered to any one of the
supports further described below, including supports containing carbon,
silica, alumina, zirconia, titania, vanadia, ceria, nitride, boron
nitride, heteropolyacids, alloys and mixtures thereof.

[0090] In one embodiment, the condensation catalyst may be derived from
the combination of MgO and Al2O3 to form a hydrotalcite
material. Another preferred material contains ZnO and Al2O3 in
the form of a zinc aluminate spinel. Yet another preferred material is a
combination of ZnO, Al2O3, and CuO. Each of these materials may
also contain an additional metal function provided by a Group VIIIB
metal, such as Pd or Pt. Such metals may be preferred when a
dehydrogenation reaction is to be carried out in concert with the aldol
condensation reaction. In one embodiment, the basic catalyst may be a
metal oxide containing Cu, Ni, Zn, V, Zr, or mixtures thereof. In another
embodiment, the basic catalyst may be a zinc aluminate metal containing
Pt, Pd Cu, Ni, or mixtures thereof.

[0091] In some embodiments, a base-catalyzed condensation reaction may be
performed using a condensation catalyst with both an acidic and basic
functionality. The acid-aldol condensation catalyst may comprise
hydrotalcite, zinc-aluminate, phosphate, Li, Na, K, Cs, B, Rb, Mg, Si,
Ca, Sr, Ba, Al, Ce, La, Sc, Y, Zr, Ti, Zn, Cr, or any combination
thereof. In further embodiments, the acid-base catalyst may also include
one or more oxides from the group of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn,
Re, Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn, Cd, P, and combinations
thereof. In an embodiment, the acid-base catalyst may include a metal
functionality provided by Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In,
Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys or combinations thereof. In
one embodiment, the catalyst further includes Zn, Cd or phosphate. In one
embodiment, the condensation catalyst may be a metal oxide containing Pd,
Pt, Cu or Ni, and even more preferably an aluminate or zirconium metal
oxide containing Mg and Cu, Pt, Pd or Ni. The acid-base catalyst may also
include a hydroxyapatite (HAP) combined with any one or more of the above
metals. The acid-base catalyst may be self-supporting or adhered to any
one of the supports further described below, including supports
containing carbon, silica, alumina, zirconia, titania, vanadia, ceria,
nitride, boron nitride, heteropolyacids, alloys and mixtures thereof.

[0092] In an embodiment, the condensation catalyst may also include
zeolites and other microporous supports that contain Group IA compounds,
such as Li, NA, K, Cs and Rb. Preferably, the Group IA material may be
present in an amount less than that required to neutralize the acidic
nature of the support. A metal function may also be provided by the
addition of group VIIIB metals, or Cu, Ga, In, Zn or Sn. In one
embodiment, the condensation catalyst may be derived from the combination
of MgO and Al2O3 to form a hydrotalcite material. Another
preferred material may contain a combination of MgO and ZrO2, or a
combination of ZnO and Al2O3. Each of these materials may also
contain an additional metal function provided by copper or a Group VIIIB
metal, such as Ni, Pd, Pt, or combinations of the foregoing.

[0093] The condensation catalyst may be self-supporting (i.e., the
catalyst does not need another material to serve as a support), or may
require a separate support suitable for suspending the catalyst in the
reactant stream. One exemplary support is silica, especially silica
having a high surface area (greater than 100 square meters per gram),
obtained by sol-gel synthesis, precipitation, or fuming. In other
embodiments, particularly when the condensation catalyst is a powder, the
catalyst system may include a binder to assist in forming the catalyst
into a desirable catalyst shape. Applicable forming processes may include
extrusion, pelletization, oil dropping, or other known processes. Zinc
oxide, alumina, and a peptizing agent may also be mixed together and
extruded to produce a formed material. After drying, this material may be
calcined at a temperature appropriate for formation of the catalytically
active phase. Other catalyst supports as known to one having ordinary
skill in the art may also be used.

[0094] In some embodiments, a dehydration catalyst, a dehydrogenation
catalyst, and the condensation catalyst may be present in the same
reactor as the reaction conditions overlap to some degree. In these
embodiments, a dehydration reaction and/or a dehydrogenation reaction may
occur substantially simultaneously with the condensation reaction. In
some embodiments, a catalyst may comprise active sites for a dehydration
reaction and/or a dehydrogenation reaction in addition to a condensation
reaction. For example, a catalyst may comprise active metals for a
dehydration reaction and/or a dehydrogenation reaction along with a
condensation reaction at separate sites on the catalyst or as alloys.
Suitable active elements may comprise any of those listed above with
respect to the dehydration catalyst, dehydrogenation catalyst, and the
condensation catalyst. Alternately, a physical mixture of dehydration,
dehydrogenation, and condensation catalysts may be employed. While not
intending to be limited by theory, it is believed that using a
condensation catalyst comprising a metal and/or an acid functionality may
assist in pushing the equilibrium limited aldol condensation reaction
towards completion. Advantageously, this may be used to effect multiple
condensation reactions with dehydration and/or dehydrogenation of
intermediates, in order to form (via condensation, dehydration, and/or
dehydrogenation) higher molecular weight oligomers as desired to produce
jet or diesel fuel.

[0095] The specific ≧C4 compounds produced in the condensation
reaction may depend on various factors, including, without limitation,
the type of oxygenated intermediates in the reactant stream, condensation
temperature, condensation pressure, the reactivity of the catalyst, and
the flow rate of the reactant stream.

[0096] In general, the condensation reaction may be carried out at a
temperature at which the thermodynamics of the proposed reaction are
favorable. For condensed phase liquid reactions, the pressure within the
reactor must be sufficient to maintain at least a portion of the
reactants in the condensed liquid phase at the reactor inlet. For vapor
phase reactions, the reaction should be carried out at a temperature
where the vapor pressure of the oxygenates is at least about 0.1 bar, and
the thermodynamics of the reaction are favorable. The condensation
temperature will vary depending upon the specific oxygenated
intermediates used, but may generally range between about 77° C.
and about 500° C. for reactions taking place in the vapor phase,
and more preferably range between about 125° C. and about
450° C. For liquid phase reactions, the condensation temperature
may range between about 5° C. and about 475° C., and the
condensation pressure may range between about 0.01 bar and about 100 bar.
Preferably, the condensation temperature may range between about
15° C. and about 300° C., or between about 15° C.
and 250° C.

[0097] Varying the factors above, as well as others, will generally result
in a modification to the specific composition and yields of the
≧C4 compounds. For example, varying the temperature and/or
pressure of the reactor system, or the particular catalyst formulations,
may result in the production of ≧C4 alcohols and/or ketones
instead of ≧C4 hydrocarbons. The ≧C4 hydrocarbon
product may also contain a variety of olefins, and alkanes of various
sizes (typically branched alkanes). Depending upon the condensation
catalyst used, the hydrocarbon product may also include aromatic and
cyclic hydrocarbon compounds. The ≧C4 hydrocarbon product may
also contain undesirably high levels of olefins, which may lead to coking
or deposits in combustion engines, or other undesirable hydrocarbon
products. In such cases, the hydrocarbons may optionally be hydrogenated
to reduce the ketones to alcohols and hydrocarbons, while the alcohols
and olefinic hydrocarbons may be reduced to alkanes, thereby forming a
more desirable hydrocarbon product having reduced levels of olefins,
aromatics or alcohols.

[0098] The condensation reactions may be carried out in any reactor of
suitable design, including continuous-flow, batch, semi-batch or
multi-system reactors, without limitation as to design, size, geometry,
flow rates, and the like. The reactor system may also use a fluidized
catalytic bed system, a swing bed system, fixed bed system, a moving bed
system, or a combination of the above. In some embodiments, bi-phasic
(e.g., liquid-liquid) and tri-phasic (e.g., liquid-liquid-solid) reactors
may be used to carry out the condensation reactions.

[0099] In a continuous flow system, the reactor system may include an
optional dehydrogenation bed adapted to produce dehydrogenated oxygenated
intermediates, an optional dehydration bed adapted to produce dehydrated
oxygenated intermediates, and a condensation bed adapted to produce
≧C4 compounds from the oxygenated intermediates. The
dehydrogenation bed may be configured to receive the reactant stream and
produce the desired oxygenated intermediates, which may have an increase
in the amount of carbonyl-containing compounds. The dehydration bed may
be configured to receive the reactant stream and produce the desired
oxygenated intermediates. The condensation bed may be configured to
receive the oxygenated intermediates for contact with the condensation
catalyst and production of the desired ≧C4 compounds. For
systems with one or more finishing steps, an additional reaction bed for
conducting the finishing process or processes may be included after the
condensation bed.

[0100] In an embodiment, the optional dehydration reaction, the optional
dehydrogenation reaction, the optional ketonization reaction, the
optional ring opening reaction, and the condensation reaction catalyst
beds may be positioned within the same reactor vessel or in separate
reactor vessels in fluid communication with each other. Each reactor
vessel preferably may include an outlet adapted to remove the product
stream from the reactor vessel. For systems with one or more finishing
steps, the finishing reaction bed or beds may be within the same reactor
vessel along with the condensation bed or in a separate reactor vessel in
fluid communication with the reactor vessel having the condensation bed.

[0101] In an embodiment, the reactor system also may include additional
outlets to allow for the removal of portions of the reactant stream to
further advance or direct the reaction to the desired reaction products,
and to allow for the collection and recycling of reaction byproducts for
use in other portions of the system. In an embodiment, the reactor system
also may include additional inlets to allow for the introduction of
supplemental materials to further advance or direct the reaction to the
desired reaction products, and to allow for the recycling of reaction
byproducts for use in other reactions.

[0102] In an embodiment, the reactor system also may include elements
which allow for the separation of the reactant stream into different
components which may find use in different reaction schemes or to simply
promote the desired reactions. For instance, a separator unit, such as a
phase separator, extractor, purifier or distillation column, may be
installed prior to the condensation step to remove water from the
reactant stream for purposes of advancing the condensation reaction to
favor the production of higher hydrocarbons. In an embodiment, a
separation unit may be installed to remove specific intermediates to
allow for the production of a desired product stream containing
hydrocarbons within a particular carbon number range, or for use as end
products or in other systems or processes.

[0104] The ≧C5 cycloalkanes and ≧C5 cycloalkenes
may have from 5 to about 30 carbon atoms and may be unsubstituted,
mono-substituted or multi-substituted. In the case of mono-substituted
and multi-substituted compounds, the substituted group may include a
branched ≧C3 alkyl, a straight chain ≧C1 alkyl, a
branched ≧C3 alkylene, a straight chain ≧C1
alkylene, a straight chain ≧C2 alkylene, an aryl group, or a
combination thereof. In one embodiment, at least one of the substituted
groups may include a branched C3-C12 alkyl, a straight chain
C1-C12 alkyl, a branched C3-C12 alkylene, a straight
chain C1-C12 alkylene, a straight chain C2-C12
alkylene, an aryl group, or a combination thereof. In yet another
embodiment, at least one of the substituted groups may include a branched
C3-C4 alkyl, a straight chain C1-C4 alkyl, a branched
C3-C4 alkylene, a straight chain C1-C4 alkylene, a
straight chain C2-C4 alkylene, an aryl group, or any
combination thereof. Examples of desirable ≧C5 cycloalkanes
and ≧C5 cycloalkenes may include, without limitation,
cyclopentane, cyclopentene, cyclohexane, cyclohexene, methylcyclopentane,
methylcyclopentene, ethylcyclopentane, ethylcyclopentene,
ethylcyclohexane, ethylcyclohexene, and isomers thereof.

[0105] Aryl groups contain an aromatic hydrocarbon in either an
unsubstituted (phenyl), mono-substituted or multi-substituted form. In
the case of mono-substituted and multi-substituted compounds, the
substituted group may include a branched ≧C3 alkyl, a
straight chain ≧C1 alkyl, a branched ≧C3
alkylene, a straight chain ≧C2 alkylene, a phenyl group, or a
combination thereof. In one embodiment, at least one of the substituted
groups may include a branched C3-C12 alkyl, a straight chain
C1-C12 alkyl, a branched C3-C12 alkylene, a straight
chain C2-C12 alkylene, a phenyl group, or any combination
thereof. In yet another embodiment, at least one of the substituted
groups may include a branched C3-C4 alkyl, a straight chain
C1-C4 alkyl, a branched C3-C4 alkylene, a straight
chain C2-C4 alkylene, a phenyl group, or any combination
thereof. Examples of various aryl compounds may include, without
limitation, benzene, toluene, xylene (dimethylbenzene), ethyl benzene,
para-xylene, meta-xylene, ortho-xylene, and C9 aromatics.

[0106] Fused aryls contain bicyclic and polycyclic aromatic hydrocarbons,
in either an unsubstituted, mono-substituted or multi-substituted form.
In the case of mono-substituted and multi-substituted compounds, the
substituted group may include a branched ≧C3 alkyl, a
straight chain ≧C1 alkyl, a branched ≧C3
alkylene, a straight chain ≧C2 alkylene, a phenyl group, or a
combination thereof. In another embodiment, at least one of the
substituted groups may include a branched C3-C4 alkyl, a
straight chain C1-C4 alkyl, a branched C3-C4
alkylene, a straight chain C2-C4 alkylene, a phenyl group, or
any combination thereof. Examples of various fused aryls may include,
without limitation, naphthalene, anthracene, tetrahydronaphthalene, and
decahydronaphthalene, indane, indene, and isomers thereof.

[0107] The moderate fractions, such as C7-C14, may be separated
for jet fuel, while heavier fractions, such as C12-C24, may be
separated for diesel use. The heaviest fractions may be used as
lubricants or cracked to produce additional gasoline and/or diesel
fractions. The ≧C4 compounds may also find use as industrial
chemicals, whether as an intermediate or an end product. For example, the
aryls toluene, xylene, ethylbenzene, para-xylene, meta-xylene, and
ortho-xylene may find use as chemical intermediates for the production of
plastics and other products. Meanwhile, C9 aromatics and fused
aryls, such as naphthalene, anthracene, tetrahydronaphthalene, and
decahydronaphthalene, may find use as solvents in industrial processes.

[0108] In an embodiment, additional processes may be used to treat the
fuel blend to remove certain components or further conform the fuel blend
to a diesel or jet fuel standard. Suitable techniques may include
hydrotreating to reduce the amount of or remove any remaining oxygen,
sulfur, or nitrogen in the fuel blend. The conditions for hydrotreating a
hydrocarbon stream are known to one of ordinary skill in the art.

[0109] In an embodiment, hydrogenation may be carried out in place of or
after the hydrotreating process to saturate at least some olefinic bonds.
In some embodiments, a hydrogenation reaction may be carried out in
concert with the aldol condensation reaction by including a metal
functional group with the aldol condensation catalyst. Such hydrogenation
may be performed to conform the fuel blend to a specific fuel standard
(e.g., a diesel fuel standard or a jet fuel standard). The hydrogenation
of the fuel blend stream may be carried out according to known
procedures, either with the continuous or batch method. The hydrogenation
reaction may be used to remove remaining carbonyl groups and/or hydroxyl
groups. In such cases, any of the hydrogenation catalysts described above
may be used. In general, the finishing step may be carried out at
finishing temperatures ranging between about 80° C. and about
250° C., and finishing pressures may range between about 5 bar and
about 150 bar. In one embodiment, the finishing step may be conducted in
the vapor phase or liquid phase, and use, external hydrogen, recycled
hydrogen, or combinations thereof, as necessary.

[0110] In an embodiment, isomerization may be used to treat the fuel blend
to introduce a desired degree of branching or other shape selectivity to
at least some components in the fuel blend. It may also be useful to
remove any impurities before the hydrocarbons are contacted with the
isomerization catalyst. The isomerization step may comprise an optional
stripping step, wherein the fuel blend from the oligomerization reaction
may be purified by stripping with water vapor or a suitable gas such as
light hydrocarbon, nitrogen or hydrogen. The optional stripping step may
be carried out in a countercurrent manner in a unit upstream of the
isomerization catalyst, wherein the gas and liquid are contacted with
each other, or before the actual isomerization reactor in a separate
stripping unit utilizing countercurrent principle.

[0111] After the optional stripping step the fuel blend may be passed to a
reactive isomerization unit comprising one or more catalyst beds. The
catalyst beds of the isomerization unit may operate either in co-current
or countercurrent manner. In the isomerization unit, the pressure may
vary between about 20 bar to about 150 bar, preferably between about 20
bar to about 100 bar, the temperature ranging between about 190°
C. and about 500° C., preferably between about 300° C. and
about 400° C. In the isomerization unit, any isomerization
catalyst known in the art may be used. In some embodiments, suitable
isomerization catalysts may contain molecular sieve and/or a metal from
Group VII and/or a carrier. In an embodiment, the isomerization catalyst
may contain SAPO-11 or SAPO41 or ZSM-22 or ZSM-23 or ferrierite and Pt,
Pd or Ni and Al2O3 or SiO2. Typical isomerization
catalysts are, for example, Pt/SAPO-11/Al2O3,
Pt/ZSM-22/Al2O3, Pt/ZSM-23/Al2O3 and
Pt/SAPO-11/SiO2.

[0112] Other factors, such as the concentration of water or undesired
oxygenated intermediates, may also effect the composition and yields of
the ≧C4 compounds, as well as the activity and stability of
the condensation catalyst. In such cases, the process may include a
dewatering step that removes a portion of the water prior to the
condensation reaction and/or the optional dehydration reaction, or a
separation unit for removal of the undesired oxygenated intermediates.
For instance, a separator unit, such as a phase separator, extractor,
purifier or distillation column, may be installed prior to the
condensation reactor so as to remove a portion of the water from the
reactant stream containing the oxygenated intermediates. A separation
unit may also be installed to remove specific oxygenated intermediates to
allow for the production of a desired product stream containing
hydrocarbons within a particular carbon range, or for use as end products
or in other systems or processes.

[0113] Thus, in one embodiment, the fuel blend produced by the processes
described herein is a hydrocarbon mixture that meets the requirements for
jet fuel (e.g., conforms with ASTM D1655). In another embodiment, the
product of the processes described herein is a hydrocarbon mixture that
comprises a fuel blend meeting the requirements for a diesel fuel (e.g.,
conforms with ASTM D975).

[0114] In another embodiment, a fuel blend comprising gasoline
hydrocarbons (i.e., a gasoline fuel) may be produced. "Gasoline
hydrocarbons" refer to hydrocarbons predominantly comprising C5-9
hydrocarbons, for example, C6-8 hydrocarbons, and having a boiling
point range from 32° C. (90° F.) to about 204° C.
(400° F.). Gasoline hydrocarbons may include, but are not limited
to, straight run gasoline, naphtha, fluidized or thermally catalytically
cracked gasoline, VB gasoline, and coker gasoline. Gasoline hydrocarbons
content is determined by ASTM Method D2887.

[0115] In yet another embodiment, the ≧C2 olefins may be
produced by catalytically reacting the oxygenated intermediates in the
presence of a dehydration catalyst at a dehydration temperature and
dehydration pressure to produce a reaction stream comprising the
≧C2 olefins. The ≧C2 olefins may comprise
straight or branched hydrocarbons containing one or more carbon-carbon
double bonds. In general, the ≧C2 olefins may contain from 2
to 8 carbon atoms, and more preferably from 3 to 5 carbon atoms. In one
embodiment, the olefins may comprise propylene, butylene, pentylene,
isomers of the foregoing, and mixtures of any two or more of the
foregoing. In another embodiment, the ≧C2 olefins may include
≧C4 olefins produced by catalytically reacting a portion of
the ≧C2 olefins over an olefin isomerization catalyst.

[0116] The dehydration catalyst may comprise a member selected from the
group consisting of an acidic alumina, aluminum phosphate, silica-alumina
phosphate, amorphous silica-alumina, aluminosilicate, zirconia, sulfated
zirconia, tungstated zirconia, tungsten carbide, molybdenum carbide,
titania, sulfated carbon, phosphated carbon, phosphated silica,
phosphated alumina, acidic resin, heteropolyacid, inorganic acid, and a
combination of any two or more of the foregoing. In one embodiment, the
dehydration catalyst may further comprise a modifier selected from the
group consisting of Ce, Y, Sc, La, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, P,
B, Bi, and a combination of any two or more of the foregoing. In another
embodiment, the dehydration catalyst may further comprise an oxide of an
element, the element selected from the group consisting of Ti, Zr, V, Nb,
Ta, Mo, Cr, W, Mn, Re, Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn, Cd, P,
and a combination of any two or more of the foregoing. In yet another
embodiment, the dehydration catalyst may further comprise a metal
selected from the group consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn,
Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of any two or
more of the foregoing, and a combination of any two or more of the
foregoing.

[0117] In yet another embodiment, the dehydration catalyst may comprise an
aluminosilicate zeolite. In some embodiments, the dehydration catalyst
may further comprise a modifier selected from the group consisting of Ga,
In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and a combination
of any two or more of the foregoing. In some embodiments, the dehydration
catalyst may further comprise a metal selected from the group consisting
of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn,
Cr, Mo, W, Sn, Os, an alloy of any two or more of the foregoing, and a
combination of any two or more of the foregoing.

[0118] In another embodiment, the dehydration catalyst may comprise a
bifunctional pentasil ring-containing aluminosilicate zeolite. In some
embodiments, the dehydration catalyst may further comprise a modifier
selected from the group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P,
Sc, Y, Ta, a lanthanide, and a combination of any two or more of the
foregoing. In some embodiments, the dehydration catalyst may further
comprise a metal selected from the group consisting of Cu, Ag, Au, Pt,
Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an
alloy of any two or more of the foregoing, and a combination of any two
or more of the foregoing.

[0119] The dehydration reaction may be conducted at a temperature and
pressure where the thermodynamics are favorable. In general, the reaction
may be performed in the vapor phase, liquid phase, or a combination of
both. In one embodiment, the dehydration temperature may range between
about 100° C. and about 500° C., and the dehydration
pressure may range between about 1 bar (absolute) and about 60 bar. In
another embodiment, the dehydration temperature may range between about
125° C. and about 450° C. In some embodiments, the
dehydration temperature may range between about 150° C. and about
350° C., and the dehydration pressure may range between about 5
bar and about 50 bar. In yet another embodiment, the dehydration
temperature may range between about 175° C. and about 325°
C.

[0120] The ≧C6 paraffins are produced by catalytically
reacting ≧C2 olefins with a stream of ≧C4
isoparaffins in the presence of an alkylation catalyst at an alkylation
temperature and alkylation pressure to produce a product stream
comprising ≧C6 paraffins. The ≧C4 isoparaffins
may include alkanes and cycloalkanes having 4 to 7 carbon atoms, such as
isobutane, isopentane, naphthenes, and higher homologues having a
tertiary carbon atom (e.g., 2-methylbutane and 2,4-dimethylpentane),
isomers of the foregoing, and mixtures of any two or more of the
foregoing. In one embodiment, the stream of ≧C4 isoparaffins
may comprise internally generated ≧C4 isoparaffins, external
≧C4 isoparaffins, recycled ≧C4 isoparaffins, or
combinations of any two or more of the foregoing.

[0121] The ≧C6 paraffins may be branched paraffins, but may
also include normal paraffins. In one version, the ≧C6
paraffins may comprise a member selected from the group consisting of a
branched C6-10 alkane, a branched C6 alkane, a branched C7
alkane, a branched C8 alkane, a branched C9 alkane, a branched
C10 alkane, or a mixture of any two or more of the foregoing. In one
version, the ≧C6 paraffins may include, for example,
dimethylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane, methylpentane,
2-methylpentane, 3-methylpentane, dimethylpentane, 2,3-dimethylpentane,
2,4-dimethylpentane, methylhexane, 2,3-dimethylhexane,
2,3,4-trimethylpentane, 2,2,4-trimethylpentane, 2,2,3-trimethylpentane,
2,3,3-trimethylpentane, dimethylhexane, or mixtures of any two or more of
the foregoing.

[0122] The alkylation catalyst may comprise a member selected from the
group of sulfuric acid, hydrofluoric acid, aluminum chloride, boron
trifluoride, solid phosphoric acid, chlorided alumina, acidic alumina,
aluminum phosphate, silica-alumina phosphate, amorphous silica-alumina,
aluminosilicate, aluminosilicate zeolite, zirconia, sulfated zirconia,
tungstated zirconia, tungsten carbide, molybdenum carbide, titania,
sulfated carbon, phosphated carbon, phosphated silica, phosphated
alumina, acidic resin, heteropolyacid, inorganic acid, and a combination
of any two or more of the foregoing. The alkylation catalyst may also
include a mixture of a mineral acid with a Friedel-Crafts metal halide,
such as aluminum bromide, and other proton donors.

[0123] In one embodiment, the alkylation catalyst may comprise an
aluminosilicate zeolite. In some embodiments, the alkylation catalyst may
further comprise a modifier selected from the group consisting of Ga, In,
Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and a combination of
any two or more of the foregoing. In some embodiments, the alkylation
catalyst may further comprise a metal selected from the group consisting
of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn,
Cr, Mo, W, Sn, Os, an alloy of any two or more of the foregoing, and a
combination of any two or more of the foregoing.

[0124] In another embodiment, the alkylation catalyst may comprise a
bifunctional pentasil ring-containing aluminosilicate zeolite. In some
embodiments, the alkylation catalyst may further comprise a modifier
selected from the group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P,
Sc, Y, Ta, a lanthanide, and a combination of any two or more of the
foregoing. In some embodiments, the alkylation catalyst may further
comprise a metal selected from the group consisting of Cu, Ag, Au, Pt,
Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an
alloy of any two or more of the foregoing, and a combination of any two
or more of the foregoing. In one version, the dehydration catalyst and
the alkylation catalyst may be atomically identical.

[0125] The alkylation reaction may be conducted at a temperature where the
thermodynamics are favorable. In general, the alkylation temperature may
range between about -20° C. and about 300° C., and the
alkylation pressure may range between about 1 bar (absolute) to 80 bar.
In some embodiments, the alkylation temperature may range between about
100° C. and about 300° C. In another version, the
alkylation temperature may range between about 0° C. and about
100° C. In yet other embodiments, the alkylation temperature may
range between about 0° C. and about 50° C. In still other
embodiments, the alkylation temperature may range between about
70° C. and about 250° C., and the alkylation pressure may
range between about 5 bar and about 80 bar. In one embodiment, the
alkylation catalyst may comprise a mineral acid or a strong acid. In
another embodiment, the alkylation catalyst may comprise a zeolite and
the alkylation temperature may be greater than about 100° C.

[0126] In an embodiment, an olefinic oligomerization reaction may
conducted. The oligomerization reaction may be carried out in any
suitable reactor configuration. Suitable configurations may include, but
are not limited to, batch reactors, semi-batch reactors, or continuous
reactor designs such as, for example, fluidized bed reactors with
external regeneration vessels. Reactor designs may include, but are not
limited to tubular reactors, fixed bed reactors, or any other reactor
type suitable for carrying out the oligomerization reaction. In an
embodiment, a continuous oligomerization process for the production of
diesel and jet fuel boiling range hydrocarbons may be carried out using
an oligomerization reactor for contacting an olefinic feed stream
comprising short chain olefins having a chain length of from 2 to 8
carbon atoms with a zeolite catalyst under elevated temperature and
pressure so as to convert the short chain olefins to a fuel blend in the
diesel boiling range. The oligomerization reactor may be operated at
relatively high pressures of about 20 bar to about 100 bar, and
temperatures ranging between about 150° C. and about 300°
C., preferably between about 200° C. to 250° C.

[0127] The resulting oligomerization stream results in a fuel blend that
may have a wide variety of products including products comprising C5
to C24 hydrocarbons. Additional processing may be used to obtain a
fuel blend meeting a desired standard. An initial separation step may be
used to generate a fuel blend with a narrower range of carbon numbers. In
an embodiment, a separation process such as a distillation process may be
used to generate a fuel blend comprising C12 to C24
hydrocarbons for further processing. The remaining hydrocarbons may be
used to produce a fuel blend for gasoline, recycled to the
oligomerization reactor, or used in additional processes. For example, a
kerosene fraction may be derived along with the diesel fraction and may
either be used as an illuminating paraffin, as a jet fuel blending
component in conventional crude or synthetic derived jet fuels, or as
reactant (especially C10 to C13 fraction) in the process to
produce LAB (Linear Alkyl Benzene). The naphtha fraction, after
hydroprocessing, may be routed to a thermal cracker for the production of
ethylene and propylene or routed to a catalytic cracker to produce
ethylene, propylene, and gasoline.

[0128] Additional processes may be used to treat the fuel blend to remove
certain components or further conform the fuel blend to a diesel or jet
fuel standard. Suitable techniques may include hydrotreating to remove
any remaining oxygen, sulfur, or nitrogen in the fuel blend.
Hydrogenation may be carried after the hydrotreating process to saturate
at least some olefinic bonds. Such hydrogenation may be performed to
conform the fuel blend to a specific fuel standard (e.g., a diesel fuel
standard or a jet fuel standard). The hydrogenation step of the fuel
blend stream may be carried out according to the known procedures, in a
continuous of batchwise manner.

[0129] To facilitate a better understanding of the present invention, the
following examples of preferred embodiments are given. In no way should
the following examples be read to limit, or to define, the scope of the
invention.

EXAMPLES

Example 1

Catalytic Reduction of Sorbitol

[0130] Catalytic reduction of 20 grams of 50 wt. % sorbitol solution was
examined in a 75-milliliter Parr5000 reactor operated at 240° C.
under 75 bar of H2 pressure, in the presence of 0.35 grams of 1.9%
Pt/zirconia catalyst modified with rhenium at Re:Pt ratio of 3.75:1. The
reaction was continued for 18 hours, before sampling the reaction mixture
via a gas chromatographic mass spectrometry (GC-MS) method using a 60
mm×0.32 mm ID DB-5 column of 1 m thickness, with 50:1 split ratio,
2 ml/min helium flow, and column oven held at 40° C. for 8
minutes, followed by a ramp to 285° C. at 10° C./min., and
a hold time of 53.5 minutes. The GC-MS results indicated greater than 90%
conversion of sorbitol to mono-oxygenates and organic acid byproducts, as
evidenced by a drop from neutral pH to 2.7. The reaction product
comprised 20.3% ethanol by weight, 25.4% 1-propanol and 2-propanol by
weight, and 2.5% dimethylketone (acetone) by weight. The presence of
acetic acid was confirmed via an HPLC method using a Bio-Rad Aminex
HPX-87H column (300 mm×7.8 mm) operated at 0.6 ml/min. of a 5 mM
sulfuric acid in water mobile phase, at an oven temperature of 30°
C., a run time of 70 minutes, and both RI and UV (320 nm) detectors.

Example 2

Digestion of Cellulosic Biomass

[0131] A digestion unit was constructed from 1/2-inch diameter by 1-foot
long 316 stainless steel tubing, heated via an electric band heater
(Gaumer Company, Inc.), and packed with 3.3-4.5 grams of nominal 1/8-inch
by 1/4-inch by 3-mm pine wood mini-chips (moisture content of 14% as
determined by overnight drying in a vacuum oven at 85° C.). A
solvent mixture was prepared to represent the principal reaction products
from hydrocatalytic reduction of sorbitol carbohydrate in Example 1. The
digestion solvent comprised 20 wt. % 2-propanol, 25 wt. % ethanol, 2 wt.
% dimethylketone, and 2 wt. % acetic acid in deionized water to give a pH
of about 2.7. For some runs, the solvent was neutralized to pH 5.4 via
addition of 1 N KOH. Solvent was fed to the digestion unit via HPLC pump
(Eldex).

[0132] The digestion unit and a product receiving vessel were pressured to
70 bar via charging the digestion unit with a solvent feed followed by
addition of hydrogen from a 90 bar supply source. Results for a series of
runs in which pH, temperatures T1 and T2, time, and solvent
flowrate were varied are shown in Table 1. In conducting the experiments,
the digestion unit and contents were heated to an initial temperature
T1 before establishing a digestion solvent feed flow at a target
flowrate between 0.07 and 0.25 ml/min. Contacting with the flowing
solvent was continued for a prescribed initial period of time, before
raising the temperature to a second temperature T2 to affect the
hydrolysis of more difficult to digest components such as cellulose.
Hydrolysate from digestion was collected in a pressurized product surge
vessel also pre-pressurized to 70 bar via addition of H2.
Backpressure control on the digestion unit and product surge vessel
enabled pressure to be maintained at 70 bar throughout the test
procedure. Analysis of the undigested wood chips at the end of the run
indicated the percent dissolution and digestion of the original wood
charge.

[0133] As shown in Table 1, only 39% of the initial wood sample was
digested for entry 4, where T2 was limited to 220° C. For all
other runs T2 was set at 240° C., and more than 70% digestion
was obtained. Digestion in excess of 90% was possible within 5.5 hours,
despite pH buffering to ˜5.4 via addition of KOH. The extent of
digestion did not correlate strongly with solvent flowrate, but was
instead primarily dependent upon time and temperature.

Example 3

Digestion Using a Sulfided Catalyst

[0134] A 1/2 inch×10-inch catalytic reactor was packed with 4.53
grams of sulfided Criterion DC2534 cobalt-molybdate catalyst containing
14% Mo and 3.5% cobalt on an alumina support. The catalyst was
pre-sulfided under flowing H2S under conditions described in CRI
publication 707/1107 Sulfiding of Tail Gas Catalyst: Proper Preparation
of Tail Gas Hydrogenation Catalyst for Long and Active Life. After
addition of 500 psig hydrogen, the reactor was heated to 255° C.
for 6.5 hours. A solution of 50 wt. % sorbitol containing 1% acetic acid,
buffered to pH 5.5 with 1N KOH, also containing 148 ppm cysteine and 1584
ppm alanine as amino acid poisons, was fed to the catalyst at
temperatures from 240° C.-260° C. for more than 70 days, at
a weight hour space velocity of 0.26. Conversion of sorbitol was
sustained at greater than 50%, despite the continuous feed of the
amino-acid containing solution.

[0135] An alternate study was conducted with 4.02 grams of a 1.9%
Pt/zirconia catalyst doped with 3.75:1 rhenium/platinum under otherwise
identical conditions. Virtually complete deactivation of the catalyst
performance was observed within 24 hours, as indicated by HPLC analysis
of unconverted sorbitol.

Example 4

Combined Digestion/Catalytic Reduction

[0136] A pilot scale flow digestion unit comprising a 1-inch outside
diameter tube×377/8 inches long, was packed with 64.0 grams of
nominal 1/4-inch softwood chips (moisture content of 34.3%). The
digestion unit was filled upflow with a digestion solvent comprising 25
wt. % 2-propanol, 20 wt. % ethanol, 2 wt. % dimethylketone, and 1 wt. %
acetic acid in deionized water. The temperature was set via electric
heater to 190° C., and ramped to 250° C. over one hour,
before reaching a final setpoint of 270° C. which was continued
for total run time of 7.8 hours. Only 7 grams of wood remained after the
digestion, indicating dissolution of 83% of the original wood feed (dry
basis).

[0137] 22.4 grams of the blended product were charged with 0.353 grams of
sulfided cobalt-molybdate catalyst (Criterion DC2534), to a 75-ml
Parr5000 Hastelloy multireactor, stirred by magnetic stir bar. The
reactor was pressured to 72 bar with hydrogen and ramped from 170°
C.-250° C. over 6 hours, before maintaining 250° C.
overnight. A companion Parr5000 experiment was conducted in 20-grams of
solvent and the same amount of sulfided cobalt molybdate catalyst, with
direct addition of 2.3 grams of softwood chips to the reactor. Product
formation (mono-oxygenates, glycols, diols, alkanes, acids) was monitored
via a gas chromatographic (GC) method "DB5-ox" using a 60-mm×0.32
mm ID DB-5 column of 1 m thickness, with 50:1 split ratio, 2 ml/min
helium flow, and column oven at 40° C. for 8 minutes, followed by
ramp to 285° C. at 10° C./min, and a hold time of 53.5
minutes. The injector temperature was set at 250° C., and detector
temperature was set at 300° C. Results indicated the conversion of
more than 35% of the original wood to mono-oxygenates and other
hydrocarbons of retention time less than sorbitol, relative to the
product formation observed with direct wood addition to the reaction
mixture.

[0138] Therefore, the present invention is well adapted to attain the ends
and advantages mentioned as well as those that are inherent therein. The
particular embodiments disclosed above are illustrative only, as the
present invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are intended
to the details of construction or design herein shown, other than as
described in the claims below. It is therefore evident that the
particular illustrative embodiments disclosed above may be altered,
combined, or modified and all such variations are considered within the
scope and spirit of the present invention. The invention illustratively
disclosed herein suitably may be practiced in the absence of any element
that is not specifically disclosed herein and/or any optional element
disclosed herein. While compositions and methods are described in terms
of "comprising," "containing," or "including" various components or
steps, the compositions and methods may also "consist essentially of" or
"consist of" the various components and steps. All numbers and ranges
disclosed above may vary by some amount. Whenever a numerical range with
a lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to about
b," or, equivalently, "from approximately a to b," or, equivalently,
"from approximately a-b") disclosed herein is to be understood to set
forth every number and range encompassed within the broader range of
values. Also, the terms in the claims have their plain, ordinary meaning
unless otherwise explicitly and clearly defined by the patentee.
Moreover, the indefinite articles "a" or "an," as used in the claims, are
defined herein to mean one or more than one of the element that it
introduces. If there is any conflict in the usages of a word or term in
this specification and one or more patent or other documents that may be
incorporated herein by reference, the definitions that are consistent
with this specification should be adopted.